
Class 

Book li'<o 

Copyright ]^^._ 

CX)F»R!GRT DEPOSIT. 



PASTEURIZATION OF MILK 

FROM THE PRACTICAL VIEWPOINT 



A HANDBOOK RELATING TO THE INSTAL- 
LATION, OPERATION AND CONTROL OF 
PASTEURIZING PLANTS. USEFUL TO 
MILK DEALERS, STUDENTS IN DAIRY 
SCHOOLS, PUBLIC OFFICIALS HAV- 
ING CONTROL OF MILK HAND- 
LING, AND OF INTEREST TO 
THE GENERAL PUBLIC 



BY 

CHAS. H. KILBOURNE 

LATE CHIEF OF THE DIVISION OF PASTEURIZING PLANTS 
NEW YORK CITY DEPARTMENT OF HEALTH 



NEW YORK 

JOHN WILEY & SONS, Inc. 
London: CHAPMAN & HALL, Limited 

1916 



5 






Copyright, 1916 
Bt Chas. H. Kilboubnb 



4i^ 



SEP 28 1916 



C!.A438t)20 



INTRODUCTION 

In presenting this book on the pasteurization 
of milk, the author has endeavored to so handle 
the subject that the milk dealers, the students in 
dairy schools, and health department officials who 
are charged M'ith the supervision and control of 
the milk sold in their communities, will find in the 
book practical assistance in their work. Except 
for the excellent bulletins issued by the United 
States Government, there are few books which deal 
with the practical aspects of milk pasteurization, 
and the author felt that a real need existed for 
such a work. 

It is possible that his long association with the 
milk work^ as it has been carried on by the New 
York City Department of Health, has somewhat 
colored his views with official conservatism. He 
has tried, however, to be fair and impartial, and to 
look at matters from the dealers' point of view. 
He has presented freely practical lessons which 

iii 



INTRODUCTION 



he has learned during a somewhat wide experience 
in investigating pasteurizing plants. 

If any dealers with questionable motives look in 
this book for practical suggestions by which they 
may be able to save milk and cream which is going 
bad, or if they wish to learn how departmental 
regulations can be evaded, they will be disap- 
pointed. 

It is hoped, however, that dealers who honestly 
desire to handle milk so that it will be safe and 
salable will find assistance in this book. 

The author wishes to acknowledge the assistance 
and good advice which he has received from Dr. 
Wm. H. Park, Dr. Chas. F. Boldune, Ole Salthe 
and James E. Thomson, and from Inspectors 
Ryan, Lee and others in the New York City De- 
partment of Health. Also he wishes to thank the 
various manufacturers of dairy machinery for in- 
formation given and illustrations supplied. 

C. H. K. 



New York, September 1, 191 6. 

iv 



The Pasteurization of Milk from the 
Practical Viewpoint 

CHAPTER I 

PASTEURIZATION IN GENERAL 

The guarding of food supplies in large towns 
and cities is one of the most important functions of 
government activity. This activity, like all forms 
of organized effort, has been a gradual develop- 
ment. In the most primitive communities, individ- 
uals naturally felt a certain care over the food 
which they ate. This interest was instinctive and 
fundamental, since each individual was conscious 
that some foods were dangerous. He therefore 
obeyed the law of self-preservation when he se- 
lected his food. 

As the homes of individuals became more con- 
gested on account of the increase in population, 
it grew to be increasingly difficult for the indi- 
vidual to select the food which he ate. He there- 
fore came to depend more and more upon the 
judgment of other people who had either used 
similar food before or else knew how it was pro- 

1 



THE PASTEURIZATION OF MILK 

duced. The substitution of the judgment of oth- 
ers for his own personal inspection of food nat- 
urally developed into a certain sort of communal 
or public control of foods. As communities be- 
came more and more congested^ it became neces- 
sary to centralize the control of foods under some 
definite organization. This centralized control, 
which was usually at first vested in some private 
organization, was later taken over by the govern- 
ment which obtained in the town or city. Thus we 
have the Boards of Food Control, which are now 
usually centered in the Health Departments. 

As the inter-dependence of the various towns and 
cities became more fully recognized, it became evi- 
dent that not only the cities but the states should 
on broad lines, regulate the production and sale of 
foods. This state regulation of foods has been cen- 
tered partially in State Health Departments, partly 
in the Agricultural Departments and sometimes in 
special departments whose duties have been to 
control the foods sold in the state. These state 
departments are becoming increasingly efficient as 
the good work which they do is becoming more and 
more recognized. 

Since the means of communication and transpor- 

2 



FROM THE PRACTICAL VIEWPOINT 



tation are becoming more rapid, the effect is that 
the world is becoming smaller, and so the consump- 
tion of foods is not confined to the states where it 
is produced. The increasing use of cold storage 
facilities for preserving foods also adds to the wide 
area from which cities and towns can obtain the 
foods which are there consumed. It, therefore, 
becomes evident that state regulation is too narrow. 
In order to properly protect the citizens, therefore, 
the general government has taken up, to a large 
extent, the control of foods which enter into inter- 
state commerce, and government standards are 
adopted. 

Among the articles of food which have perhaps 
received the largest share of attention we find milk. 
This attention has been deserved on account of the 
almost universal use of milk, and also on account 
of the fact that it becomes easily infected with 
dangerous bacteria, and having become infected it 
is itself an ideally good medium for their growth. 
The milk thus becomes so changed or decomposed 
that it is frequently unsafe for food. The oppor- 
tunities for infection are many, on account of the 
many persons through whose hands it passes be- 
fore it reaches the city consumer, and where it is 



THE PASTEURIZATION OF MILK 

perhaps fed to the children who depend upon milk 
for their life. At any point along the line of 
travel from the cow to the consumer it may be- 
come dangerously infected. If the cows from 
which it is drawn are not healthy, the milk may 
start on its journey in an unsafe condition. Even 
if it is perfectly wholesome when drawn from the 
cows, it may at any point along its line of travel 
become changed from its natural state. 

Disease-producing bacteria or other less harm- 
ful germs may enter the milk from stable dust or 
from the manure and urine which drops from the 
cow herself. The milk bottles and cans may have 
been carelessly washed or the water with which 
the washing is done may be from contaminated 
sources. Diseased, or unclean persons may be em- 
ployed in milking the cows, or in handling the 
milk after it is drawn. Cans or bottles in which 
the milk is placed may have been returned from 
the consumer in filthy condition and have been 
again used for containing fresh milk before being 
thoroughly washed and sterilized. Contagious dis- 
ease may have been in the homes from which they 
are returned. 

Much of the milk in large cities is handled at 

4 



FROM THE PRACTICAL VIEWPOINT 

creameries or shipping stations which arc located 
in the country and from which the milk is shipped 
to the cities. Thus, there is an added opportu- 
nity for milk infection on account of the insani- 
tary buildings or from coming in contact with 
dust-laden air or diseased employees. Once hav- 
ing gained access to the milk the growth and mul- 
tiplication of the germs is aided by the powerful 
agencies of age and heat. If germs which pro- 
duce disease get into the milk the danger that epi- 
demics of disease will occur is a serious one. Each 
point in the handling of milk is therefore an im- 
portant point, for the chain of milk safety is only 
as strong as its weakest link. 

Aside from the danger of bacterial contamina- 
tion there is of course the possibility of actual 
adulteration being practised within the legal defini- 
tion of that term. Foreign substances may be 
added, such as water, coloring matter, preserva- 
tives, etc., or the cream may be removed. Such 
adulteration may be accidental or it may be de- 
liberately practised, with "malice aforethought," 
with intent to deceive and defraud the final con- 
sumer, for the purpose of increasing the profits. 
On account of the sharp competition which ex- 

5 



THE PASTEURIZATION OF MILK 

ists in modern trade, some dealers consider that 
tliey are justified in doing some things which are 
objected to by public boards of control. Some- 
times milkmen will endeavor to save a perishable 
product by the use of preservatives. This form of 
adulteration, however, is at present very little 
practised. 

The importance which attaches to the public or 
communal control of milk is not the only force 
which is lifting to a higher level the character of 
the milk sold to the public. Milk dealers them- 
selves are realizing more and more that modern 
conditions are such that only the best and the 
most efficiently produced and handled product can 
remain in the market. They are therefore be- 
coming more and more active in establishing 
means for effectively controlling their own sup- 
plies. The methods employed are various. Asso- 
ciations of men have been formed, the object of 
which is to secure mutually useful advice and to 
give each other the benefits of individual expe- 
riences. 

The larger dealers establish within their own 
organizations an efficient inspection service and 
seek by means of laboratory tests and research 

6 



FROM THE PRACTICAL VIEWPOINT 

work to study their problems and so secure the 
best milk possible at the least expense, and with 
the least amount of waste. Thus the governmen- 
tal forces and the dealers themselves both work 
toward the goal of a better milk supply. 

The great importance of the problems which 
affect the securing of a safe milk supply has led 
to the publication of many books, in which the va- 
rious phases of the matter have been considered. 
The composition of the milk, its chemical charac- 
teristics, the number and kind of bacteria con- 
tained, the forms of adulteration which occur and 
the methods for detecting such adulteration have 
all been broadly covered. The relation of milk to 
the public health and the disease epidemics which 
have been due to infected milk have received large 
attention in published works. Much has also been 
published regarding the most effective methods to 
be employed in the public control of milk supply. 

While there is an extensive literature concern- 
ing the problems of milk pasteurization dealing 
with the matter from the theoretical side, and also 
covering certain special phases of the work, it is 
rather surprising to find how little of this is 
available for the practical use of the milkman who 

7 



THE PASTEURIZATION OF MILK 

wishes to install pasteurizing apparatus and to so 
handle his output that the most efficient service 
can be secured with the least possible expense. 
This dearth of literature has been no doubt largely 
due to the fact that the information which the 
many practical men have gained in their experi- 
ments has never been so brought together that it is 
available for the use of those who are seeking 
knowledge along practical lines. That this should 
be so is but natural, for several reasons. 

First: The manufacturers who are interested in 
emphasizing the good points of their apparatus 
are not inclined to call attention to their defects. 

Second: Milk dealers who, through experiments 
in trying out various forms of apparatus have 
learned what appears to be best suited to their 
needs, are not inclined to publish to the world 
information which has cost them much time and 
money to secure. Should they do so, they would 
be benefitting their competitors. 

Third: Public officials in city, state or national 
public service, who have made many inspections, 
conducted tests and carried on extensive research 
work are comparatively few. In fact, in very few 
cities is the field for observation sufficiently exten- 

8 



FROM THE PRACTICAL VIEWPOINT 



sive to enable such officials to draw unbiased or 
broad conclusions. State officials are as yet doing 
little work along these lines. The general govern- 
ment has been and is now carrying on extensive 
and valuable experimental work^ and as a result 
much useful and valuable information has been 
published.* 

The writer has published some matter which his 
experience has taught him.f Dr. Rosenau lias 
devoted considerable space to the subject of milk 
pasteurization and has given much valuable infor- 
mation on the subject.]; 

Additional information which is of considerable 
value has been acquired by the experience of the 
writer and other inspectors in the New York City 
Department of Health, working in conjunction 
with the laboratories. It seems to be proper that 
this information could be available to the general 
public. 

As before stated, the application of heat to per- 
ishable foods in order to preserve them from de- 



*Ayers and Johnson, Bureau of Animal Industry — Circular 
184 and other pubHcations. 

fN.Y.C. Department of Health Reprint Series Nos. 1 and 27. 
JThe Milk Question by M. J. Rosenau. 

9 



THE PASTEURIZATION OF MILK 

cay has probably been practised since the discov- 
ery of fire. The earliest record of the application 
of heat to food in a scientific way was in 1872, 
when Sheele, the well-known Swedish chemist, 
discovered that vinegar could be preserved against 
spoiling by heating it. Soon after this other peo- 
ple began to preserve fruits, vegetables, milk, etc., 
by heating them in closed vessels. No scientific ex- 
planation, however, of the reason why the heating 
process preserves these foods appeared until I860 
to 1870, when Pasteur, in his studies as to the 
causes for the deterioration which took place in 
wines and beers, discovered that there was certain 
forms of life previously unknown whose unchecked 
growth gave to liquor its bad flavors, etc. These 
were termed by Pasteur "diseases." He discovered 
that by heating beer and wine to a temperature of 
158° to 176° F., and holding the fluids at these 
temperatures for a period of time, the "disease 
germs," as he called them, were destroyed and the 
flavor of the liquor was improved, the loss by 
spoiling being at the same time prevented. 

This discovery was of immense financial benefit 
to Europe, and in consequence the heating of wines 
and beers became very generally practised, the 

10 



FROM THE PRACTICAL VIEWPOINT 



process being termed "pasteurization," from the 
name of the man who originated it. At the present 
time, no brewery is considered to be well equipped 
and up to date unless extensive apparatus is em- 
ployed to heat the product before it is placed upon 
the market. 

The thought that the same principle might be 
applied to the preservation of milk on an exten- 
sive scale had its birth in Europe, and it is claimed 
that the first commercial milk pasteurizer was 
made by Ahlborn in Hildeshein, Germany, in 1880, 
and that a similar apparatus was made in the same 
year by Fresca in Berlin, Germany. The process 
was later adopted in Denmark, where dairying has 
reached such a high degree of perfection. 

At all events, the machine now known as the 
Danish pasteurizer was introduced into this coun- 
try by Reid about 1895, and is now sold under 
various names by different manufacturers. Modi- 
fications and developments of the original idea 
form the basis of nearly all the pasteurizing ma- 
chines used at the present time. 

This form is illustrated in Figs. 1 and 2, and is 
described more in detail later in this book. 

In Denmark the object sought by the use of the 

11 



THE PASTEURIZATION OF MILK 

pasteurizer was the improvement of the flavor and 
quality of butter, the manufacture of which is such 
an important industry in that country. The pas- 
teurization of the cream used for butter is there 
generally practised, and it is subsequently ripened 
by the introduction of a pure culture grown in the 
laboratories in order to secure the most desirable 
texture and flavor. These methods have resulted 
in the production of a butter in Denmark which is 
considered to be a standard article. The indus- 
try has grown remarkably and its products are 
shipped to England and other parts of Europe in 
normal times, and have also, in times of shortage, 
been shipped to the United States. 

When it became appreciated in Denmark that 
the spread of bovine tuberculosis was a danger- 
ous menace to the dairy industry, a law was passed 
requiring that milk whey, etc., which was fed to 
calves, swine and other animals must be heated 
before being fed in order to prevent the spread of 
this disease among the growing stock. This 
proved so useful in accomplishing its object, that 
similar laws have been passed in various states in 
this country. Vermont and Pennsylvania have 
such laws in the East. Strange to say, many of 

12 



FROM THE PRACTICAL VIEWPOINT 

the dairymen object to this^ much preferring the 
unheated skim milk. The dangers are not gen- 
erally appreciated. 

It became apparent to some people that that 
which was good for preventing disease among cat- 
tle would also be useful in preserving health 
among children, and in 1 866 Soxhlet advocated that 
milk which was fed to infants be heated. About 
this time, Jacobi, the distinguished American pedi- 
atrist, advised the boiling of milk fed to infants. 
In 1869 he referred to the apparatus devised by 
Soxhlet, this being the first American reference 
to the subject. This was before it was so well 
known, as is now generally accepted, that milk is 
a means of carrying infectious diseases, such as 
diphtheria, typhoid, scarlet fever, etc. Jacobi found 
that children fed upon boiled milk were less liable 
to have intestinal disorders, and his long and con- 
tinued success in treating children tends to dis- 
credit the assertions made by some that the pas- 
teurization of milk at comparatively low tempera- 
tures destroys its nutritive value and is injurious 
to children. Jacobi still advocates the boiling of 
milk. 

It was soon brought to the attention of milk 

IS 



THE PASTEURIZATION OF MILK 

dealers that milk which was old and liable to be- 
come a commercial loss on accomit of souring 
could be saved if it were heated, and that the fer- 
mentation due to the growth of the enormous num- 
ber of bacteria in milk could thus be checked. 
Milk which had been handled in an unclean man- 
ner, or which had been badly cooled by insuffi- 
cient icing, or which it became necessary to hold 
for a long time before sale, could still be made 
marketable by rapidly heating and cooling it. Lit- 
tle attention, however, was paid to the matter of a 
uniform heating of the milk, or to the exact degree 
of temperature to which it was subjected. Almost 
no attention was directed to the destruction of 
pathogenic bacteria. These, in fact, were little un- 
derstood by the milk dealers, and few dealers main- 
tained laboratories for studying milk problems. 

On account of the questionable motives which 
actuated dealers in adopting this method of milk 
treatment, as well as the faulty methods employed, 
health authorities, as a rule, at first looked upon 
the pasteurization of milk with disfavor. It was 
considered that the process was a makeshift and 
simply used as a means of covering up bad prac- 
tices in the production and handling of milk. In- 

14 



FROM THE PRACTICAL VIEWPOINT 



stead of encouraging the pasturization of milk, or 
even ignoring it, health authorities rather took 
steps to discourage its practice. The desire to se- 
cure a safe milk supply for the public took form 
in strenuous efforts to clean up the sources from 
which the milk was secured, to secure proper re- 
frigeration and to assure clean handling. The cry 
was for clean milk as produced from the dairies, 
and the process of pasteurization was frowned 
upon. 

In New York and other cities, commendable 
progress was made in the effort to secure a clean, 
safe raw milk, and the improvement made in the 
conditions under which milk is handled, particu- 
larly in receiving stations and creameries, can 
hardly be appreciated by those who were unfa- 
miliar with conditions before the campaign for 
clean milk was inaugurated. Dairy conditions 
have also been greatly improved, and the dairymen 
themselves repeatedly say that they would not for 
any consideration go back to old conditions. All 
efforts made to advance the production of clean 
milk should be continued with unabated vigor. 

It soon became apparent, however, that the se- 
curing for a large city of a raw milk supply 

15 



THE PASTEURIZATION OF MILK 

which could be guaranteed to be reasonably clean 
and safe was practically impossible. If it was se- 
cured, it would involve the expenditure of an enor- 
mous amount of money and energy, which the tax- 
payers would not approve, and it was seen that it 
might result in so much added expense to pro- 
ducers and dealers that the price of milk to the 
consumer would be greatly increased, perhaps to 
such an extent that the sale of this valuable uni- 
versal food would be seriously curtailed. 

Public health administrators were at length led 
to the conclusion that the pasteurization of milk 
was the only practical means of securing a sup- 
ply which would be reasonably safeguarded against 
dangerous infection. By many persons it was con- 
sidered to be a makeshift, and it is still so re- 
garded by some authorities, it being held by them 
that its employment should only be continued until 
a clean, safe raw supply can be secured. Others, 
and by far the majority of authorities, are, how- 
ever, convinced that pasteurization will always be 
a necessity, and that even the best of raw milk 
should be provided with the additional safeguard 
which will be secured by pasteurization. 

It is even urged by some that certified milk, 

16 



FROM THE PRACTICAL VIEWPOINT 

which is the safest raw milk possible to be ob- 
tained, should be pasteurized before being used for 
infant feeding. This thought has been strength- 
ened by information of comparatively recent dis- 
covery, that milk may become infected through 
coming in contact with persons who harbor dis- 
ease germs, but who are not in any way ill. These 
persons are therefore perfectly innocent of any 
knowledge that they are a source of infection to 
milk, and thus a dangerous and insidious menace 
to the milk consumer. It has been found that cer- 
tain persons may be, and not infrequently are, in- 
fected with typhoid bacilli, without they themselves 
knowing that they are thus infected. Such per- 
sons are known as typhoid carriers. Other persons 
harbor the germs of diphtheria in mouth and 
throat, without having any symptoms of the dis- 
ease whatever. Such persons may handle milk and 
unwittingly infect it. 

Within the last few years there have been in 
different cities epidemics of septic sore throat. 
These have occurred in Boston, Baltimore, Chi- 
cago, etc. In Boston in 1911 several thousand 
persons were made ill by milk coming from a 
farm where the milk was exceptionally well cared 

17 



THE PASTEURIZATION OF MILK 

for.* Many of the persons thus affected died. 
In 1912 a similar epidemic occurred in Baltimore, 
where many persons were made sick and many 
deaths occurred. This was traced to milk infec- 
tion, f Had these milks been properly pasteur- 
ized, these epidemics of disease would probably 
have been avoided. 

Aside from the foregoing considerations, the 
fact that a very considerable percentage of cows 
producing milk are tuberculous gives an added 
reason why it is desirable to heat the milk be- 
fore use. There has been much misapprehension 
in the public mind regarding the actual danger 
which threatens human beings from this source. 
There seems to be no doubt that these dangers, 
while real, have been somewhat exaggerated. In 
the first place, the fact that a cow may be seri- 
ously affected with tuberculosis does not make it 
certain that her milk is dangerous to use. If 
proper care is exercised while the milk is being 
drawn from the cow, none of the germs will get 



*Winslow, C. E. A., Journal of Infectious Diseases, Volume X 

No. 1, January, 1912. 

tPublic Health Reports, November 22, 1912. 

18 



FROM THE PRACTICAL VIEWPOINT 

into the milk. Of course, if the disease existed in the 
udder of the cow, or in the milk ducts, there would 
then be direct contamination of the milk as it was 
drawn. Cows more frequently, however, have the 
disease in the lungs or other parts of the body, in 
which case the germs will pass through the alimen- 
tary tract and be voided with the urine and faeces. 
If the cows are allowed to become badly soiled, 
particles of manure and dirt, carrying with them 
the tubercle bacilli, will inevitably fall into the 
milk, thus infecting it. It is also possible that 
dried manure in stables where tubercular cattle 
are kept will produce dust, which, when stirred 
up by the movements of the cattle or by persons 
and by sweeping, may fall into the milk. This 
danger is probably more imaginary than real, 
since recent experiments by the Geneva Experi- 
ment Station * indicate that stable dust plays a 
part in milk infection which is of comparatively 
little importance. It is also true that the exposure 
of manure to light and air for a length of time 
sufficient to produce a dry dust would tend to de- 
stroy the tubercle bacilli. The amount of infec- 



*Bul. 409. N. Y. Ag. Exp. Sta. 

19 



THE PASTEURIZATION OF MILK 

tion would be therefore comparatively small. It 
is also a known fact that while tubercle bacilli will 
live in milk, they will not multiply. 

The apprehension experienced by many persons 
that they may be infected with tuberculosis from 
the milk which they consume should be lessened 
by their knowledge of this further fact, namely, 
that tuberculosis of the bovine type with which 
cattle are affected is rarely infectious to human 
beings who are over fifteen years of age, and 
rarely causes fatal tuberculosis in children over 
five years old. The careful examination of hun- 
dreds of cases where death has occurred from 
tuberculosis among children appears to conclu- 
sively show that the danger of infection from bo- 
vine tuberculosis is largely limited to persons 
under fifteen years of age. Of deaths from tuber- 
culous affections of persons under this age, only 
10 per cent, had tuberculosis of the bovine type. 
This has been determined for New York City by 
investigations carried on by Park and his col- 
leagues, extending over several years, and the same 
conclusions have been reached by European sci- 
entists. 

The records of New York City for the years 

20 



FROM THE PRACTICAL VIEWPOINT 

1913-1914-1915 show the following interesting 
facts : 

Deaths of Children Under Fifteen Years. 

1913 1914 1915 

From all causes... 23,574 22,312 23,031 
From all tubercular 

diseases 1,288 1,166 1,200 

10 per cent of these 
latter figures in- 
dicate 128.8 116.6 120. 

These represent the number of persons who died 
in these years from tuberculosis which was prob- 
ably of bovine type. 

This means that out of every 1,000 deaths from 
all causes of children under fifteen years of age, 
5.4 in 1913, 4.8 in 1914, and 5.2 in 1915, had 
tuberculosis which was probably of the bovine 
type. 

While it is possible that bovine tuberculosis may 
reach human beings through infected meat or by 
direct infection from dust, dirt, etc., it is probable 
that most of it is due to infected milk. 

There are many cases of tuberculosis existing 

21 



THE PASTEURIZATION OF MILK 

in bones and glands which do not result fatally. 
Nearly one-half of these are thought to be of the 
bovine type, and very likely have their origin in 
milk. 

It is evident, therefore, that while the danger of 
tubercular infection from milk when expressed in 
terms of percentages is comparatively slight, there 
appears to be, nevertheless, a definite danger to 
children from this source, and the safeguarding of 
this milk by pasteurization is extremely desirable. 

Rosenau * places tuberculosis first among the 
diseases carried by milk, thus considering it a 
greater menace than typhoid fever. 

All these facts have induced most health authori- 
ties to change their attitude toward the pasteuriz- 
ing of milk for general use, and it is now the ex- 
ception instead of the rule to find persons familiar 
with the subject who favor the use of raw milk, 
except when it is from dairies which are abso- 
lutely above suspicion. 

The important consideration which influences 
authorities when they insist that milk be pasteur- 
ized is of course the desire that the milk may be 
free from dangerous bacteria. 

*The Milk Question — M. J. Rosenau. 

22 



FROM THE PRACTICAL VIEWPOINT 

There are commercial reasons which influence 
dealers, such as the desire to prevent the souring, 
and thus the loss of milk, but these considerations 
have little weight with health authorities. The 
prevention of economic waste of food products has 
a bearing upon the public health, and there are 
indications that the personal interest which those 
in authority have as men in these matters is being 
extended to their oflficial interest. Care must be 
observed, however, that these two considerations be 
justly balanced. 

The United States Government has endeavored 
to reduce the losses which result from the condem- 
nation of cream which is not considered fit to use 
as cream. This is accomplished by partially de- 
naturing it by the addition of salt, so that it can be 
used for butter making. An attempt has also been 
made to prevent the destruction of milk which has 
a temperature above that fixed by the authorities 
as legal. It is well known that in some cities this 
drastic action is taken in order to secure proper 
refrigeration. Such destruction of milk, which has 
a high food value, should be looked upon as almost 
criminal. 

Careful experiments carried on by Park, Rose- 

23 



THE PASTEURIZATION OF MILK 

nau, and others have demonstrated the fact that 
if milk is heated to a temperature of 140° F._, and 
is held at this temperature for twenty minutes, or 
even less, all of the pathogenic or disease-produc- 
ing bacteria will be destroyed. Also, if the milk 
is heated to a uniform temperature of 158° F., 
and held thereat for one minute, all such disease 
germs will be killed. Between these extremes, dif- 
ferent degrees of temperature, and correspond- 
ingly varying lengths of holding time, will pro- 
duce equally good results. These experiments 
have been carried on of course in laboratories 
where ideal conditions for securing accurate re- 
sults existed. Accurate temperatures could be ob- 
tained and the length of time for which the milk 
was held could be carefully controlled. When, 
however, pasteurization is carried on under com- 
mercial conditions, where large quantities of milk 
are handled, the same amount of accuracy is not 
possible. There are variations in temperature and 
variations in the length of time for which it is 
held, due largely to the mechanical defects or 
limitations in all forms of machinery. These fac- 
tors of error render the results uncertain, and it 
is therefore desirable that the temperatures and 

24 



FROM THE PRACTICAL VIEWPOINT 

the lengths of time for holding, which in the labo- 
ratory tests have been found to be effective, be 
somewhat increased, in commercial practice. 

Various cities have made regulations in this re- 
spect which appear to best suit local conditions. 
In New York City, when regulations were first 
adopted concerning milk pasteurization, the length 
of time for which milk must be held when heated 
to 158° F. was officially fixed at no less than three 
minutes, and if heated to 140° it must be held for 
at least twenty minutes. Between these extremes 
of temperature holding times were fixed which va- 
ried between three minutes and twenty minutes. 

Experiments were made by Schores and Rose- 
nau * in which careful tests were carried on while 
milk was being pasteurized in the ordinary way, 
a commercial pasteurizer and holding device being 
used. These tests were made for the purpose of 
determining if the thermal death point of patho- 
genic bacteria, as indicated by laboratory tests, 
could be safely relied upon under commercial con- 
ditions. In their experiments the investigators in- 
troduced germs of tuberculosis, diphtheria, and 
typhoid fever, into milk, which was then run 

♦The Journal of Medical Research Vol. XXVI No. 1. 

25 



THE PASTEURIZATION OF MILK 

through a commercial pasteurizer and heated to 
different temperatures_, and held for varying lengths 
of time. The results obtained indicated that when 
an attempt was made to heat this milk in a com- 
mercial pasteurizer to a temperature of 140° F., and 
then hold it for twenty minutes, there was a con- 
siderable unavoidable variation in the actual tem- 
perature to which the machine was capable of 
heating the milk. This was due to the difficulties 
of both hand and automatic temperature control. 
Even with the best automatic controller, it is 
probable that the real variation of temperature is 
greater than is indicated upon the record charts. 
Thermometers are not usually sufficiently sensitive 
to record rapid fluctuations in temperature. It is 
also true that thermometers indicate average tem- 
peratures only, and it is possible that certain por- 
tions of the milk, the temperature of which is con- 
siderably below this indicated average, pass 
through the apparatus. 

In regard to the time held also, especially when 
a continuous or flow type holding apparatus is 
used, great uncertainty exists. It is impossible to 
be sure that the time is the same as intended. The 
rate of flow varies, and there is also more or less 

26 



FROM THE PRACTICAL VIEWPOINT 

mixing of the milk due to various causes^ which 
will be discussed later. 

Schores and Rosenau found that pathogenic bac- 
teria were not all killed when the factors of tem- 
perature and time were attempted which had been 
found effective in laboratory tests. They there- 
fore recommended, in order to provide a sufficient 
margin of safety, that all milk he heated to a 
temperature of at least 145°, and there held for 
no less than twenty-five minutes. This opinion is 
shared by most persons who have made a study 
of the subject. The New York City Department 
of Health, in 1914, so modified its regulations as 
to require that pasteurized milk be heated to from 
142° to 145° F. for at least thirty minutes. 

While the destruction of all pathogenic bac- 
teria in milk is the primary concern of health au- 
thorities, there are certain other considerations 
which have weight with them, and among these 
is the effect which heat has upon the chemical 
characteristics of the milk. It has been found that 
when milk is heated to say l60° F. or over, some 
of the constituent parts of the milk are changed in 
such a way as to make it somewhat inferior as a 
food, especially for infants. These changes have 

27 



THE PASTEURIZATION OF MILK 

been somewhat extensively studied by the United 
States Government experts^ and it has been found 
that as the temperature rises above 160° F., these 
changes take place to an increasing extent, and at 
the boiling point quite extensive changes are ob- 
served. At this temperature, the milk sugar be- 
comes scorched, the casein and the albumin are 
somewhat hardened, the calcium, magnesium and 
phosphoric salts are partially precipitated, all of 
which renders the milk less easily digested. It 
therefore follows that the lowest temperature 
which is consistent with the destruction of the 
pathogenic bacteria is the most desirable. 

It is also true that milk which contains an ex- 
cessive number of bacteria carries with it, as a re- 
sult of their growth, certain by-products, such as 
acids and other undesirable substances, and may 
also contain dangerous poisons. Rosenau states 
that the known poisons which are produced by the 
growth of bacteria in milk are very few, but that 
such poisons may possibly exist and produce harm- 
ful effects upon the persons using the milk. These 
by-products of bacterial grovrth in milk are not 
entirely destroyed by heating, even when the boil- 
ing temperature is attained. For this reason it is 

28 



FROM THE PRACTICAL VIEWPOINT 

desirable that milk which is to be pasteurized shall, 
before it is heated, be as free as possible from all 
bacteria. It is this consideration which has led 
health authorities to insist that the milk before pas- 
teurization shall not contain an excessive number 
of bacteria. 

Milk dealers know that their customers com- 
monly judge of the richness of the milk by the 
amount of cream which appears upon the top of 
the bottle. For this reason the showing of a 
"good cream line" is one of the things for which 
the milk dealer strives. In some parts of Europe 
the cream is thoroughly mixed in the milk by 
homogenizing it, so that the cream will not rise, 
but the American housewife is not educated to this 
custom, and therefore anything which interferes 
with the apparent volume of cream on the milk is 
a stumbling-block to the milk dealer. It has been 
found that milk which is heated to a temperature 
of 148° F. or over and is held for any consid- 
erable period of time, will have its cream line de- 
stroyed, or at least be made indistinct. When 
milk is heated to a temperature lower than this 
and is held for a great length of time, the same 
effect is produced. There are other reasons which 

29 



THE PASTEURIZATION OF MILK 

interfere with the cream line which will be dis- 
cussed later. 

Another objection which customers urge against 
pasteurized milk is that it has a distinctly 
scorched or cooked taste. This is undoubtedly true 
when the milk is heated to a high temperature, or 
when an uneven temperature is maintained. If the 
heating medium is kept at a point greatly above 
the temperature to which the milk is to be raised, 
the same effect is produced. On account of this 
cooked taste it is evident that there is a commer- 
cial objection to pasteurization where it is not 
properly or carefully done. 

Moreover, when a low temperature of heating is 
used, the enzymes are not much affected, while 
they are destroyed when a high temperature is ap- 
plied. Indeed, the Storch test, which is used to 
determine whether skim milk has been heated to 
165° or higher in compliance with the laws in this 
regard, depends upon the non-action of the en- 
zymes. These are destroyed by high heating. 
This test is of little or no value in testing milk 
pasteurized at low temperature. 

Since an even heating at comparatively low 
temperatures and a holding for a long time secures 

30 



FROM THE PRACTICAL VIEWPOINT 

the desired result in the destruction of bacteria, 
and at the same time produces none of the unde- 
sirable effects which follow when, a high tem- 
perature is employed, it is evident that this 
method of procedure is that which is much to be 
preferred. 

To summarize the considerations which have 
just been discussed, it is evident that the pastur- 
ized milk which most nearly fulfills the require- 
ments desired by health authorities, and at the 
same presents, from the commercial aspect, the 
least objections, must conform to the following de- 
mands : 

First: Before pasteurization it must contain only 
a small number of bacteria. 

Second: When it is heated it must be subjected 
to a temperature which destroys all pathogenic or 
disease-producing bacteria, and also a large per- 
centage of bacteria of all other kinds. 

Third: Its constituents must be very little 
changed or altered by excessive heating. Its nu- 
tritive value must not be impaired, and its diges- 
tive enzymes must be uninjured. 

Fourth: The taste of the milk must not be no- 
ticeably changed. 

31 



THE PASTEURIZATION OP MILK 

Fifth: The apparent volume of cream must not 
be reduced. 

In so far as these factors represent results 
which are properly demanded by health authori- 
ties, there are, broadly speaking, two general 
methods by which they can be controlled when 
their control depends upon the powers exercised 
by the municipality or the state. One of these 
may be called the laboratory method, and the 
other the inspectional method. When the labora- 
tory method is employed it is necessary that cer- 
tain definite chemical and bacteriological standards 
be adopted, which apply to pasteurized milk or to 
milk which is to be pasteurized. Some of these 
standards may depend upon color reactions. Such 
standards being in force, the effectiveness of con- 
trol depends upon the frequent examination of sam- 
ples of milk taken before and during the process 
of pasteurization and as it is offered for sale. If 
the tests show that the milk conforms to the legal 
standards, it may be judged, with a fair degree of 
confidence, that the apparatus employed in pas- 
teurizing and handling the milk is properly in- 
stalled and operated. 

When the inspectional method of control is em- 

S2 



FROM THE PRACTICAL VIEWPOINT 

ployed, it is necessary that certain definite regula- 
tions be adopted which shall specify on broad lines 
the form of apparatus which must be used, how 
it shall be installed and how it shall be operated. 
The construction and arrangement of the build- 
ings and of the various rooms may be specified, it 
having been determined by previous experience 
that such and such apparatus and surroundings 
operated and handled in such and such a way will 
produce milk which will be of the character de- 
sired. With these regulations in force, it is pos- 
sible, by frequent and careful inspections made of 
pasteurizing plants, to determine whether or not 
the legal regulations are being faithfully observed. 
If it is found that they are complied with, then it 
is logical and safe to conclude that the milk pro- 
duced is of suitable character, and will satisfac- 
torily respond to all suitable chemical and bac- 
teriological tests which may be applied. 

As a matter of fact, neither method of control 
is used by authorities to the exclusion of the other, 
but a combination of the two methods is found to 
be the most satisfactory. In some cities the em- 
phasis is placed upon laboratory tests, with in- 
spections made to confirm the results. In other 



THE PASTEURIZATION OF MILK 

places, the emphasis is upon physical regulations 
and inspections, with occasional laboratory tests to 
confirm the conclusions reached and to aid in the 
discovery of obscure defects which may escape ob- 
servation during the usual inspections. No advice 
can be given as to which method is most desirable 
without first knowing local conditions, taking into 
account the extent of the milk industry, the avail- 
able factors of men, money and laboratory equip- 
ment, etc. Each community presents its individ- 
ual problem. 

Health authorities are often requested by milk 
dealers to give advice as to the form of pasteurizing 
apparatus which will perform the best work, or 
they are asked what kind of machine the authorities 
recommend. It is manifestly improper for health 
authorities to recommend specifically any one or 
more forms of apparatus as the best. If they did, 
they would lay themselves open to the charge of 
unfair favoritism, and to the suspicion that im- 
proper influence determined their judgment. It 
is only proper that they should state that in their 
experience certain forms of apparatus, operated 
in certain ways, have performed certain things in 
actual practice which are or are not satisfactory 



FROM THE PRACTICAL VIEWPOINT 

to those who are responsible for this condition of 
the milk. Indeed, when advice is asked as to the 
form of apparatus most desirable to be installed 
at a given point, it is impossible to solve such a 
problem without possessing complete knowledge of 
the conditions which surround each plant where it 
is desired to install a pasteurizer. Each plant 
presents an individual problem of its own, which 
must be carefully studied, having clearly in mind 
all the facts which specially relate to the plant in 
question. It is impossible to place too much em- 
phasis upon this point, since time and money and 
the securing of expert advice before the construc- 
tion and equipment of a plant will frequently bring 
continuous dividends in convenience, in the saving 
of time, in preventing needless waste of money, 
and in the general satisfaction which accompanies 
the successful operation of an efficient plant. 

Among the factors to be considered, the con- 
struction and physical characteristics of the build- 
ing where the plant is to be located is of impor- 
tance in determining the selection of the appara- 
tus to be used. Again^ the distance of the plant 
from the point where the milk is to be distributed 
and consumed should be considered. If located 

S5 



THE PASTEURIZATION OF MILK 

in the country at a distance from the city, the ele- 
ment of time available after the milk is delivered 
by the dairyman is also an important item. The 
amomit of milk to be pasturized daily, and the 
use which is to be made of the finished product 
have a bearing upon the final decision. With 
many dealers the question of expense may be of 
first importance, but it must be borne in mind 
that cheap installation does not always mean econ- 
omy. The question of expense involves both the 
initial cost of installation and the outlay for oper- 
ation and upkeep. Where the matter of furnish- 
ing sufficient steam is a point for serious con- 
sideration, or where water expense affects the final 
cost, it is desirable to use those forms of appara- 
tus which consume the fewest heat units and which 
use the least amount of water. There are also 
other considerations which will be discussed later, 
and it will be found that at many plants unique 
conditions exist which must be carefully studied. 

On broad lines, however, it may be stated that 
a pasteurizing plant, in order to be as nearly as 
possible ideal in regard to its construction, and 
which will at the same time be capable of produc- 
ing a milk which will be satisfactory from the 

36 



FROM THE PRACTICAL VIEWPOINT 

standpoint of safety and wholesomeness, and will 
also satisfy commercial demands, should combine 
the following features: 

1. 2'he Building. — The building where the plant 
is located should contain ample space and should, 
if possible, be so arranged that the milk will flow 
by gravity from the point of receipt, or where 
cans are emptied to the point where it is taken out 
for delivery or transportation. 

2. Separate Rooms. — The various stages in the 
process of treating the milk, such as receiving, 
pasteurizing, cooling, filling containers, storage 
and of washing the containers, should be carried 
on in separate, clean, well-lighted and ventilated 
rooms or compartments. 

3. Protection from Contamination. — At all 
points during the process of handling, the milk 
should be protected against contamination from 
contact with unclean apparatus, and from infec- 
tion by means of dust-laden air. This protection 
is especially necessary after the holding process 
is completed. Any infection occurring after this 
time is not corrected by heating, and may there- 
fore be a source of danger. 

4. Constant Temperature. — The heating appa- 

«7 



THE PASTEURIZATION OF MILK 

ratus, whatever its form, should be capable of 
heating every particle of milk to a temperature 
which will never be below that to which it is the 
intention that it shall be heated. For instance, 
if it is intended to heat to 140°, the temperature 
should not fluctuate between 135° and 145°, but 
should remain constantly at 140° or over. 

5. Method of Heating. — The heating should be 
accomplished by an apparatus which allows the 
milk to flow over a clean metal surface, which is 
kept hot by means of heated water, and not by 
direct steam contact. This hot water should never 
have a temperature more than 10° or 15° higher 
than that to which it is desired to heat the milk. 

6. Holding Apparatus. — The holding appara- 
tus, whether the absolute or the continuous flow 
type process is employed, should be so constructed 
and operated that it will definitely insure the 
holding of every particle of the milk without fail 
for the desired length of time. 

7. Recorders. — The temperature to which the 
milk is heated must be automatically recorded, and 
should be automatically controlled. It is desir- 
able that a temperature recording device be in- 
stalled at the point where the milk leaves the 

58 



FROM THE PRACTICAL VIEWPOINT 

heating apparatus and that another recorder be 
attached to the outlet pipe from the holder. This 
latter recorder indicates whether or not any great 
amount of heat has been lost during the holding 
process^ and also shows whether the apparatus is 
thoroughly heated before the milk is admitted. If 
not so heated, the first milk leaving the holder 
will have been somewhat cooled, and the recorder 
will indicate this. After the apparatus has been 
in operation for a considerable time, it will then 
acquire the temperature of the milk, which will 
then pass out with the temperature but little di- 
minished. These observations do not apply to a 
tank or batch pasteurizer. In this case a single 
recorder attached to the tank itself shows all that 
is necessary. It also indicates the time for which 
the milk is held at the required temperature. 

8. Pumps and Pipings. — The amount of milk 
piping in use should be reduced to the minimum 
requirements. All piping which is used should 
be of sanitary construction, with the joints and 
turns so arranged that they can be easily taken 
apart for cleaning. As before stated, the appara- 
tus should be so arranged that the milk will flow 
by gravity from point to point in the process of 

S9 



THE PASTEURIZATION OF MILK 

treatment. If, however, it is necessary to use milk 
pumps, they should be of absolutely sanitary con- 
struction. The use of pumps for moving the raw 
milk is less objectionable than is their use for mov- 
ing pasteurized milk. Not only is the danger of 
infection by means of unclean pumps very serious, 
but if the milk is pumped while hot, the cream is 
so disturbed that it does not rise as readily as is 
desirable. 

9. Rubber Fittings and Gaskets. — The use of 
rubber fittings, of gaskets and of stuffing-boxes 
should be avoided. 

10. Cooling. — The milk should be immediately 
and rapidly cooled, to a temperature as nearly 
40° F. as possible. This cooling should be accom- 
plished within thirty minutes after the heating and 
holding process is completed. Except where cool- 
ing is carried on in the tanks where it is heated, 
the cooling can be completed in much less than 
thirty minutes. The milk should be, of course, 
kept cold until delivered to the consumer. 

11. Cleaning of Containers. — All containers, 
including cans, covers and bottles, should be com- 
pletely and if possible automatically washed and 
sterilized. They should then be thoroughly dried 

40 



FROM THE PRACTICAL VIEWPOINT 

and should be stored in clean, cold rooms, and there 
kept inverted or carefully covered until filled. 

12. Cleaning of Apparatus. — All apparatus 
used in handling milk should be carefully washed 
and sterilized after its use, and all of it which 
comes in contact with the pasteurized product 
should be again sterilized before its use each day. 

13. Healthy Employees. — All persons employed 
in handling the milk should be known to be healthy 
and free from any infectious disease. They 
should be clean in their person and habits, and 
should wear special clean clothing, preferably of 
white material, while handling milk. 

lit. Bottle Capping. — The milk bottles, after 
filling, should be capped by clean machinery, thus 
avoiding as far as possible any personal contact 
with the milk after it is pasteurized. 

It is needless to say that all the ordinary precau- 
tions regarding the sanitary construction of build- 
ings where food is handled should be observed, 
and the close proximity of stables or other con- 
taminating influences should be avoided. 

There are, of course, many other points of de- 
tail in the construction and operation of pasteur- 
izing plants which will repay careful attention. 

41 



THE PASTEURIZATION OF MILK 

These will be touched upon in the following pages. 
On broad lines, however, it may be said that if the 
foregoing conditions are carefully fulfilled, then 
it will be possible to obtain a good safe milk which 
the public may consume with a feeling of security, 
and which should satisfy all requirements of health 
authorities. 

It is not proper, of course, to recommend any 
specific type or form of apparatus to be used in 
pasteurizing milk. It is proposed, however, to de- 
scribe in the following pages and to show by dia- 
gram or illustration the construction and operation 
of different makes of apparatus, and to call atten- 
tion to those points in each which experience has 
taught are of advantage or disadvantage. 



42 



CHAPTER II 



HEATERS 



In 1909 the New York City Department of 
Health first adopted the rule which required that 
milk could not be considered as pasteurized un- 
less it had been heated to a definite temperature 
and held at this temperature for a certain definite 
length of time. New York was the pioneer in 
requirements of this sort. 

At this time various forms of milk heaters were 
on the market, but no device was available for 
holding the heated milk. All heaters employed 
a process which is known as the continuous or flash 
process of heating. By this process the milk 
flowed or was forced in a continuous stream 
through the apparatus, where it was subjected to 
an amount of heat which was not very definite, and 
which was controlled by the hand of the operator. 
The milk was then immediately cooled. 

Most of the forms of apparatus which were 
then on the market are still in use, and certain new 
forms of heaters have been invented. Certain new 
types of apparatus were devised as adjuncts of 

43 



THE PASTEURIZATION OF MILK 

the heaters, into which the milk was allowed to 
flow from the heaters and in which the hot milk 
was held for the time required by the regulations. 

As before stated, the forms of heaters in use 
in 1909 are still employed, with certain new forms 
made by many different manufacturers. They are 
all comprised under some one of five typical forms, 
as follows: 

First Type. — The so-called Danish heater is 
sold by various firms. It is shown in the accom- 
panying illustrations (Figs. 1 and 2). This is 
the oldest form of heater in use in this country. 
In this form a large central cylinder is provided 
with a double cover or jacket. The space between 
the inner and outer shell is filled with water, into 
which steam is introduced. By means of a 
suitable device the steam is distributed through the 
water at various points. 

In operation, the milk is allowed to flow or is 
pumped into the inner compartment or cylinder, 
and by means of rapidly revolving paddles it is 
thrown by centrifugal force against the inner sur- 
face of the cylinder. This surface is kept hot by 
means of the hot water and steam in the outer 
shell. The milk enters at the bottom of the cylin- 

44 



FROM THE PRACTICAL VIEWPOINT 




Fig. 1 



Fig. 2 



der, and since the outlet pipe at the top is placed 
at a tangent to the cylinder^ the rotating paddles 
tend to throw the milk out of the pipe. The ma- 
chine therefore acts somewhat as a pump, and 
when the whole machine is set at an angle from 
the perpendicular, this tendency to throw the milk 
is enhanced and the milk can be lifted about fifteen 
feet. This fact is one of the advantages of the 
machine. Another advantage is that it is com- 
paratively inexpensive, since it is rather small. Its 

45 



THE PASTEURIZATION OF MILK 

size also tends toward the ease of cleaning, there 
being no great amount of surface with which the 
milk comes in contact. 

This very fact, however, that the heating sur- 
face is small in area, is also a disadvantage, for 
it renders it necessary to raise the temperature of 
the heating medium to a point so high that it is 
frequently very much in excess of that to which 
it is the desire to heat the milk. The result is 
that certain portions of the milk reach a tempera- 
ture so high that a distinctly scorched taste is im- 
parted to it. This taste persists in the entire 
body of the treated milk, even though the average 
temperature of the milk leaving the apparatus is 
below 145°. This is especially noticeable if the 
flow of milk into the apparatus fluctuates. It can 
be readily seen that with a very hot heating sur- 
face, and at the same time a small amount of milk 
passing through the machine due to a sudden stop- 
page of flow, this milk would attain a high tem- 
perature. 

This superheating of even a portion of the milk 
tends to cause an interference with the normal 
rising of the cream, after the milk is placed in 
containers. The vigorous agitation of the hot milk 

46 



FROM THE PRACTICAL VIEWPOINT 

by means of the paddles also has a tendency to 
break up the fat globules into smallei particles, 
which do not so readily rise to the surface. 

It is difficult to maintain a uniform temperature 
with this type of machine, since the amount of 
heating fluid is comparatively small, and when 
there is either a fluctuating flow of milk or a vary- 
ing milk temperature, there is no automatic con- 
troller which can be made to respond to sudden 
changes in temperature quickly enough to check 
or increase the flow of steam into the heating 
chamber. 

As a general proposition, also, the introduction 
of steam directly into a heating chamber is to be 
avoided, since there is always the possibility that 
certain portions of the steam will strike the heat- 
ing surface before becoming condensed, and will 
therefore heat these portions to an abnormally 
high point. 

Second Type. — There are several heating de- 
vices made by different firms, and having certain 
variations in the details of their construction, 
which embody the same general principles. These 
are illustrated in Figs. 3, 4, 5. In all of these 
the milk flows between two or more upright, heated 

47 



THE PASTEURIZATION OF MILK 




Fig. 3 

1 — Discharge of warmed milk to gathering tank. 

2 — Return of warmed milk to interior of heater. 

3 — Discharge of heated milk to holder. 

4 — Hot water intake. 

5 — Return of held milk to regenerator. 

6 — Cold milk entering heater. 

7 — Discharge of partly cooled miik to cooler. 

48 



FROM THE PRACTICAL VIEWPOINT 




THE PASTEURIZATION OF MILK 




Fig. 4-B 



cylindrical surfaces. The heating surfaces are 
kept at the desired temperature by means of hot 
water, which in turn is heated either by the intro- 
duction of steam into the water chamber directly, 
or by heating the water in tanks outside the milk 

50 



FROM THE PRACTICAL VIEWPOINT 



Milk 
Outlets 




Fig. 5 

1 — Interior water tank. 
2 — Exterior water tank. 
3 — Space between water tanks, through which milk is forced upward. 

51 



THE PASTEURIZATION OF MILK 

apparatus. From these tanks it is pumped into 
the heating chambers. Where steam enters di- 
rectly into the milk apparatus the same objections 
obtain which were noticed in the description of the 
Danish type of heater. Superheating of the milk 
in whole or in part, an objectionable cooked taste, 
interference with the cream line, etc., are likely to 
follow. Where an outside heating tank is employed, 
it is comparatively easy to keep the water at a 
nearly uniform temperture by means of a thermo- 
stat, which controls the introduction of steam. 
With this heated water being pumped to the milk- 
heating apparatus, it is certain that the milk can 
never get above the temperature to which the water 
is heated, and if this water is not more than 10° or 
15° hotter than the temperature at which it is the 
intention to heat the milk, no serious superheating 
can result. This point will be more fully de- 
scribed later. 

In all heaters of this type some method is em- 
ployed to keep the milk in constant motion as it 
flows upward between the heating surfaces, thus 
insuring that all portions of milk come in contact 
with their surfaces. In the machine illustrated in 
Fig. 3 this agitation is accomplished by means of 

52 



FROM THE PRACTICAL VIEWPOINT 

a revolving arm, which extends into the milk space 
between the inner and the outer water chambers. 
In Fig. 5 J the inner cylinder revolves and the nar- 
row corrugation which extends in a spiral form 
around the cylinder forces the milk upward. The 
shaft which operates these stirring devices in some 
instances comes in contact with the milk, and in 
order to prevent leakage, it is necessary to pro- 
vide some sort of packing or stuffing box. This 
is a disadvantage, since nearly all packing is some- 
what porous, and it is difficult to keep clean. 

Heaters constructed in this general form have 
been found to be effective in operation, and good 
results have been obtained by their use. They 
have been found to be durable as well. Some in- 
dividual machines have been in use for ten years, 
which indicates the carefulness with which they 
have been constructed. Those forms of heaters 
are the most satisfactory in which the greatest 
amount of heating surface is available, and where 
the amount of hot water which circulates through 
the apparatus is relatively large. These conditions 
render it possible to use water which has a com- 
paratively low temperature. 

Some of these heaters employ what is known 

53 



THE PASTEURIZATION OF MILK 

as the "regenerative principle." This means that 
the hot milk which flows from the machine is em- 
ployed for warming the cold milk which flows into 
the apparatus to be heated. When this regenera- 
tive principle is used, a considerable economic sav- 
ing of heat units is secured. This saving means 
that less steam is required for heating, and also that 
less ice is necessary for cooling. In the type illus- 
trated in Fig. 4 the milk flowing from the holder 
is conveyed to a holding apparatus, and after be- 
ing held is returned to the heater, where it flows 
through another compartment and helps to heat 
the inflowing cold milk. 

At least one form of regenerative heater (Fig. 
6) is so constructed that this intermediate holding 
process cannot be used. In sections of the country, 
therefore, where city regulations require that the 
heated milk be held for a definite period, this form 
of heater cannot be used. As a so-called "flash" 
pasteurizer, this machine has given good results. 

In Fig. 4-B is shown a form of heater in which 
the hot water is contained on the inside of the lower 
cone. The milk flows from the top over the heated 
cone. Revolving arms to which is attached a heavy 
cord, keep the cone surface wiped, and prevent 

.54 



FROM THE PRACTICAL VIEWPOINT 




d 

M 




55 



THE PASTEURIZATION OF MILK 

the milk from sticking to the heated surface. 
There is difficulty in keeping the cord clean and 
sanitary. 

Third Type. — The tubular type of heater is 
manufactured and sold by several concerns. In 
all of these forms, the milk flows through tubes, 
which are themselves surrounded by some heating 
medium, usually hot water. In the form shown 
in Fig. 7 the milk tube is enclosed by a larger 
tube, through which hot water flows in a direction 
opposite to the milk flow. In forms which are 
illustrated by Figs. 8, 9 and 10 the heating water 
is contained in boiler-like structures, through 
which the tubes extend. Care must be exercised 
in order to make sure that there can be no leak- 
age between the milk tubes and the water con- 
tainers. In Fig. 7 the couplings between the vari- 
ous milk pipes in the series are outside of and 
beyond the water couplings, so that no mixing of 
the milk and water can occur unless there is a 
broken milk pipe. In Figs. 8, 9 and 10 the milk 
tubes are either braized or expanded into the heads, 
and the danger of leakage is slight. Of course, 
when heat is applied to these tubes, the tendency 
is for them to expand and so become more tightly 

5Q 



FROM THE PRACTICAL VIEWPOINT 




Fig. 7 



fixed in the heads. Sudden and wide variations of 
temperature would tend to loosen the joints. The 
flowage of the water in a direction opposite to milk 
flow brings the hottest water against those milk 
tubes where the hottest milk is found. As the 

57 



THE PASTEURIZATION OF MILK 




Fig. 8 



water flows along the tubes it becomes gradually 
cooled by the cooler milk^ so that it emerges at a 
low temperature. Thus the milk is heated grad- 
ually, and no sudden raising of the temperature 
occurs. This renders the control of the tempera- 
ture an easy matter, since sudden fluctuation in 
temperature cannot readily occur. There is also 

58 



FROM THE PRACTICAL VIEWPOINT 




Fig. 9 



an economical use of the heat, and little of it is 
wasted. 

In Fig. 11 a form of heater is illustrated in 
which the milk flows through a group of small 
tubes, which are themselves enclosed in a large 

59 



THE PASTEURIZATION OF MILK 




60 



FROM THE PRACTICAL VIEWPOINT 




THE PASTEURIZATION OF MILK 

tube. The larger tube contains the water which 
surrounds the small tubes which contain the milk. 
When the regenerative principle referred to is em- 
ployed, in this type of heater the hot milk return- 
ing from the holding tanks is allowed to flow 
through the larger tube, and thus assist in heating 
the cold inflowing milk. 

Tubular heaters are doing very satisfactory 
work. Those machines are in some respects the 
most efficient in which the flow of milk is slow 
enough or which have a sufficient heating surface 
to insure that all portions of the milk will reach 
the maximum temperature. It has been found 
from experience that when milk flows through 
tubes which are of comparatively large diameter, 
there is a tendency for that portion of the milk 
which is in the center of the tube to flow faster 
than that which is close to the inner surface of 
the tube. This is due to the greater friction at 
the point of contact. It can be readily seen that 
there will therefore be a tendency for the milk 
which flows more slowly close to the heated surface 
of the tube to become heated to a considerably 
higher point than that near the center. When 
the water entering the final tube of the heater is 

62 



FROM THE PRACTICAL VIEWPOINT 

high in temperature, there is a certain amount of 
danger of cooking or scorching the milk, and pos- 
sibly of breaking up the fat globules. It is also 
true that if a coating of cooked milk forms on the 
inner surface of the tube, it acts as an insulating 
material and therefore a constantly increasing tem- 
perature must be applied to the water. The return 
of the milk from one tube to another in the series 
tends to mix the milk and so break up the more 
rapid flowing core. This breaking up process, 
however, may have a detrimental effect upon the 
fat content and may render the cream less likely 
to rise. In one or two instances known to the 
writer it was found that when the milk left the 
apparatus at a temperature of only 140° the cream 
line was considerably interfered with. 

The types shown in Figs. 7, 10 and 11 have this 
advantage, namely, that since they can be obtained 
in sections, the pasteurizing plant can be expanded 
by the installation of additional sections as the 
growth of the business demands. Since a cooling 
apparatus of exactly similar form is provided it is 
possible to extend the cooling facilities in the same 
way. By a proper interchange of the water used 
in both the heater and cooler, the regenerative 

63 



THE PASTEURIZATION OF MILK 

principle is made use of, and the cool water leav- 
ing the heater is carried over to the cooler, so that 
it helps to cool the hot milk flowing into it. 

In choosing a machine of this type, care should 
be exercised in securing one which may be easily 
cleaned, especially at the turns and joints. All 
these should be smooth and readily accessible. 

It should be borne in mind that while a large 
heating area with many pipes is an advantage in 
securing an even heating with a low water tem- 
perature, the difficulties of cleaning are also in- 
creased. 

It is also readily seen that when powerful pumps 
force the hot water rapidly through the heating 
pipes, a relatively lower heating temperature may 
be employed. 

An objection to the tubular form of heater lies 
in the fact that the tubes in this system are nearly 
'liorizontal and parallel. There is thus but little 
inclination or pitch to the tubes, and the milk flows 
from them rather slowly when they are emptied at 
the close of operations for the day. This objec- 
tion has been overcome in some of the more re- 
cently manufactured machines, by putting the 
pipes at an incline and not parallel to each other. 

64s 



FROM THE PRACTICAL VIEWPOINT 



Thus the milk can be more readily drained from 
the apparatus when it is being emptied. 

One striking advantage of the tubular type of 
apparatus is found in the fact that it may be very 
thoroughly sterilized. Steam can be admitted into 
all the parts where the milk will enter, and the 
steam may be under pressure if so desired. 

It is important that a machine of this type be 
so constructed that no milk will leak from one 
section of tubing into another section, but that it 
all follows the course which it is intended that it 
shall follow. In the forms shown in Figs. 8, 9 
and 10, the doors at the ends which cover the ends 
of the milk tubes are provided with gaskets to 
prevent this leakage. 

It is well to note whether or not these gaskets 
are tight. In one or two forms, the gaskets con- 
sist of sheets of metal which are backed by felt 
or rubber in such a way that the metal readily 
conforms to the projections of the tubes, thus mak- 
ing a closely fitting cover. The metal sheet can, 
of course, be readily cleaned. 

Fourth Type. — The tank, or so-called batch sys- 
tem of heating milk, is quite largely employed. 
Heating tanks for this purpose are now manu- 

Q5 



THE PASTEURIZATION OF MILK 




66 



FROM THE PRACTICAL VIEWPOINT 




Fig. 13 



factored by many concerns which handle pasteur- 
izing apparatus. These batch pasteurizers consist, 
as shown in Figs. 12, 13, 14-, 14-B, 15, 1 6, of hori- 
zontal tanks, constructed sometimes singly and 
sometimes made with two compartments in the same 
apparatus. In Fig. 16 we see a tank which is in the 
form of an upright cylinder. These tanks are in 
some cases surrounded by an insulating jacket. 
In others there is an open space between the inner 
and outer shell, through which hot water is made 

67 



THE PASTEURIZATION OF MILK 







68 



FROM THE PRACTICAL VIEWPOINT 




THE PASTEURIZATION OF MILK 

to circulate, usually by means of a pump. These 
tanks have, extending through them in a horizon- 
tal direction, some form of agitator. This may be 
a tubular coil, as in Figs. 12, 13 and 14-B, or stir- 
ring paddles, as in Fig. 15, or it may be coil sus- 
pended from above, as in Fig. l6. Some of the 
older forms have, instead of a coil of pipe, a series 
of hollow screw-shaped discs. In some, as in Fig. 
14, there is a tubular structure which is suspended 
from the top of the tank and which swings back 
and forth by means of a mechanical arrangement. 
In operation, these tanks being filled with milk, 
hot water is forced through the tubes or discs 
above referred to. These coils rotate, keep the 
milk mixed and, at the same time, heat it and thus 
raise it to the desired temperature. The circulation 
of water is maintained in some machines by means 
of pumps, the steam for heating being admitted 
into the return water shortly before it is again 
forced through the coil. 

In other machines, as in Fig. 12, the admission 
of air into the coil creates a suction which forces 
the water through without the use of pumps. In 
the form shown in Fig. 15, the heating is accom- 
plished in a rather novel manner. In the space 

70 



FROM THE PRACTICAL VIEWPOINT 





6 



71 



THE PASTEURIZATION OF MILK 

between the inner and outer shell, there are placed 
near the top two perforated pipes, into which hot 
water is forced. The water is thrown through 
the perforations, in jets, against the outer surface 
of the inner shell. It flows down, following the 
contour of the tank, and drops from the bot- 
tom, from whence it is again pumped through 
the pipes after being reheated. The milk in the 
meantime is kept in agitation by means of the 
paddles. 

In any of these tanks it usually requires from 
fifteen minutes to twenty-five minutes to raise the 
milk from 50° to a temperature of 145°. The 
proper temperature having been attained, the steam 
is shut off, and the milk is allowed to remain hot 
in the tank for any desired length of time. 

The tank form of pasteurizer in practice shows 
excellent results. In plants where there are large 
quantities of milk to be pasteurized it is necessary 
that two, three or more tanks be arranged in se- 
ries. This insures a continuous flow of milk 
through the cooling apparatus and the filling de- 
vices. In actual operation with three tanks, it 
occurs that while one tank is being emptied after 
heating and holding, the milk is being held in the 

72 



FROM THE PRACTICAL VIEWPOINT 

second tank, while in the third tank the milk is 
flowing in and is being heated. These operations 
are repeated in rotation. 

Many tests have shown that if the water in the 
heating coils is heated by injecting steam directly 
into the heating coil, the temperature at the inlet 
end is rarely above l65°. It may occasionally 
reach 175°. Usually it is sufficiently low so that 
the milk is not injured by superheating. It can be 
readily seen that the temperature at the inlet end 
of the coil is much greater than at the outlet end, 
since the cold milk takes up the heat, therefore the 
heating efficiency of the coil is not equally great 
for its entire length. Some attempts have been 
made to improve matters by placing a smaller per- 
forated coil inside the larger pipe, so that the 
water distributed through the coil would have the 
same temperature in its entire length. 

An objection to the submerged coil is that it be- 
comes necessary to have the bearings packed with 
some sort of a stuffing-box. Stuffiing-boxes are 
always a source of possible danger both on account 
of the absorption of milk, which renders cleaning 
difficult, and on account of the fact that the con- 
stant attrition of the metal at the point of bearing 

7S 



THE PASTEURIZATION OF MILK 

creates a condition whereby a metallic taste may- 
be imparted to the milk. 

In the form shown in Fig. 15 the objections 
due to uneven heat distribution are at least partly 
overcome, since the heat is the same at both ends 
and on both sides of the tank. 

In Figs. 15 and 16 there are no bearings in the 
milk, and stuffing-boxes are therefore eliminated. 

It is obvious that when pumps of large capacity 
force the water rapidly through the coils, the tem- 
perature will be more nearly uniform throughout 
the entire length, and a lower initial temperature 
can be employed. 

In plants where a comparatively small amount 
of milk is to be pasteurized, as frequently occurs 
in country shipping stations, one or two tanks will 
hold all the milk which is received at a plant each 
day. It is therefore possible to use the tank for 
several purposes. First, as a dumping tank for 
receiving the milk; second, as a heater; third, as 
a holding apparatus; fourth, as a cooler, since by 
replacing the hot water by ice water or brine in 
the coils, the milk can be cooled in the same tank. 
Fifth, cans can be filled directly from these tanks. 
In using the tank as a cooler, however, it is found 

74 



FROM THE PRACTICAL VIEWPOINT 




Fig. 16 



75 



THE PASTEURIZATION OF MILK 

that the time required is usually considerably over 
thirty minutes, which is longer than most authori- 
ties will allow. In some instances the writer has 
found that from an hour to an hour and a half 
was required. Where brine can be circulated rap- 
idly through the coil, this time can be considerably 
reduced, especially if the coil is large. Some spe- 
cial tanks are provided with unusually large coils. 
In plants which are at a considerable distance 
from the point where the milk is consumed, the 
tank system of pasteurizing has this added advan- 
tage. It is not always possible to get the milk into 
the creamery from the patrons and to pasteurize 
it before the departure of the milk train. In some 
localities the regulations of the authorities specify 
that pasteurized milk must be sold within from 
twenty-four to thirty-six hours after pasteuriza- 
tion. At these distant points it therefore becomes 
necessary to hold over some raw milk from day to 
day. If a pasteurizing system other than the tank 
system is employed, this raw milk is stored in 
cans, and a considerable amount of extra labor is 
required to handle them. If the tank is used, the 
milk which is received on one day may be placed 
in the tank and there stored till the following 

76 



FROM THE PRACTICAL VIEWPOINT 

morning, it being kept cold in the meantime by 
the circulation of cold water through the coils. 
This milk may be heated on the morning of pas- 
teurization as early as necessary to get it ready 
for shipment, no handling or transfer of the milk 
being previously necessary. 

In case the tank is used as both a heater and a 
cooler, there is of course a considerable strain 
upon the joints of the apparatus due to the expan- 
sion and contraction of the metal. Those forms of 
apparatus are therefore the most desirable which 
are the most strongly constructed, and are there- 
fore least liable to break. A coil of pipe is 
stronger than a screw disc. 

Fifth Type. — Another process which has been 
used to a limited extent for pasteurized milk is 
known as bottle pasteurizing. By this method, the 
bottles are filled with cold milk and are hermeti- 
cally sealed. They are then either placed in a 
tank, where they are submerged in water, or else 
they are carried under showers of water. In either 
case the temperature of the water increases as 
the bottles are carried forward. When the de- 
sired temperature is reached, the bottles are then 
held for the desired time and are then brought 

77 



THE PASTEURIZATION OF MILK 



in contact with cold water, either in tanks or 
in showers, till the temperature is sufficiently 
reduced. 

There is little doubt that from the purely theo- 
retical point of view the pasteurization of milk in 
the bottle is the ideal method. During the process 
not only the bacteria contained in the milk are de- 
stroyed, but also whatever bacteria may have been 
contained in the bottles and on the caps are also 
killed. It can also be seen that the danger of 
recontamination after pasteurization is reduced to 
the minimum. 

There are several forms of apparatus on the 
market in which the pasteurization takes place in 
the bottle, two of which are shown in Figs. 17 and 
18. This method of treatment is very extensively 
used in the manufacture of beer. In Fig. 17, the 
cases filled with bottles of the milk are carried by 
an endless chain conveyor through several tanks 
of water in succession. The water in the first tank 
is warm, is hotter in the next, and so on till the 
maximum is reached, after which the milk is car- 
ried into the cooling tanks. The entire process 
requires an hour or more. 

In the process shown in Fig. 18, an endless plat- 

78 



FROM THE PRACTICAL VIEWPOINT 




Fig. 17 



:W^>y^'^r/^^'^ 



79 



THE PASTEURIZATION OF MILK 




Fig. 18 



form carries the cases of bottles under showers of 
water, of varying temperatures. 

When milk is pasteurized by this method, a more 
complete cooling is necessary than is the case with 

80 



FROM THE PRACTICAL VIEWPOINT 

beer. More cooling tanks or additional showers 
are therefore required. 

In a rather new machine, not shown in this book, 
the bottles are placed in a thoroughly insulated box 
or compartment, where they are subjected to a 
shower of water, the temperature of which is in- 
creased or decreased at will by proper regulating 
devices on the outside of the apparatus. It is 
claimed that with this outfit the heating and cool- 
ing is rapidly accomplished, and that the com- 
plete insulation of the compartment prevents the 
loss of heat. It is also said that, for the same rea- 
son, the same apparatus can be used as a cold 
storage box, and the treated milk can be allowed 
to remain in the apparatus after the completion 
of the process till it is ready to be taken out for 
delivery. These claims would seem to make it an 
especially desirable outfit for small dealers, and 
for dairymen in or near the cities where the milk 
is to be sold. 

The objections which are advanced against 
the process of bottle pasteurization are, f,rst, that 
the cap which it is necessary to use upon the bot- 
tles in order to secure a tight seal is expensive; 
too much so to warrant its use upon milk which is 

81 



THE PASTEURIZATION OF MILK 

sold at tlie popular price. It can, however, be 
used on bottles containing milk sold at advanced 
prices, like Certified Milk, Grade A, etc. The 
second objection is that since the milk expands 
upon being heated, the bottles cannot be entirely 
filled. The bottles must therefore be made of a 
size especially large, and customers must be 
taught that bottles which are not full do still in 
fact contain the full measure of milk. A third 
objection advanced has been that milk in bottles 
which are not full is more likely to become shaken 
up, and the cream disturbed, than is the case in 
bottles completely filled. This objection is 
probably not of serious moment. A fourth and 
rather serious objection is that the expense in the 
consumption of heat units is much greater than 
when other methods of pasteurizing are employed. 
The reason for this is that the mass of glass in 
the bottle nearly equals the mass of the milk, and 
that since both bottle and milk must be heated 
and also cooled, nearly double the amount of heat 
is necessary, and a proportionately great amount 
of cooling medium is used. In large plants this 
added expense is very considerable. 

An attempt has been made to overcome this last 

82 



FROM THE PRACTICAL VIEWPOINT 

objection, in part at least, by providing a series 
of tanks shown in Fig. IQ. The five tanks shown 
in line No. 1, 2, 3, 4, 5 are used for containing 
the cases of filled bottles which are to be heated. 
These are lowered into the tanks by suitable de- 
vices. The other three tanks behind the pas- 
teurizing tanks contain the water to be used in the 
process. One, A, contains hot water, which is 
kept at a constant temperature by means of a 
thermostat. From this tank the water is circu- 
lated by means of a pump through the tank, which 
at the time contains the bottles which are being 
heated and held. 

A second tank, C, contains cold water, which is 
kept cold either by ice or by a brine coil. This 
water is circulated by a pump through the pas- 
teurizing tank, in which at the time are contained 
the bottles which were being cooled. 

The third tank, C, is called a tempering tank. 
The water in this is used for regenerative pur- 
poses, in the following manner: After a tank full 
of bottles has been heated and held for the de- 
sired length of time, the hot water is all returned 
to the heating tank, rendering the bottle tank 
empty of water. Cool water from the tempering 

83 



THE PASTEURIZATION OF MILK 

tank is then admitted. This cools the hot bottles 
of milk to a certain extent, and is in turn partly 
heated. The water is then returned to the tem- 
pering tank, after which the cold water from tank 
C is pumped into the tank full of partially cooled 
bottles, and when the cooling is complete, the bot- 
tles are removed, and the tank is filled with fresh, 
unpasteurized bottled milk. The warm water from 
the tempering tank, then being admitted, it begins 
to warm the cold bottles and is itself cooled. 
After its return to the tempering tank it is ready 
to be used again in the routine which has been 
described, the process being repeated indefinitely. 
In this way a large amount of heat is saved which 
would be otherwise wasted. 

From the illustration and the description the im- 
pression is gained that this apparatus would be 
rather cumbersome to operate, although it would 
no doubt be possible to somewhat simplify the me- 
chanical arrangements for shifting the water from 
tank to tank. The writer is not personally fa- 
miliar with any plant where such an arrangement 
is in use. 

Another method has been devised for saving 
some of the heat otherwise wasted. This consists 

84 



FROM THE PRACTICAL VIEWPOINT 




r— ( 
6 



85 



THE PASTEURIZATION OF MILK 

in heating the milk in any good form of pasteuriz- 
ing apparatus, and then pouring it, while hot, into* 
bottles which have just emerged in a hot condition 
from this sterilizing apparatus. The heat which 
is usually lost in cooling the hot bottles is in this 
way saved. Since, however, the bottles must in 
any case be cooled, it can be seen that the cooling, 
which usually takes place slowly in the air when 
washed bottles are stored in the ordinary way, 
must now be accomplished rapidly in order to re- 
duce the milk to the proper temperature in the 
time required. This necessitates the use of ice 
water or brine refrigeration, and since the volume 
of glass used equals the volume of the milk, dou- 
ble the amount of cooling medium is required than 
when only the milk is cooled. 

Experiments were made by Ayers and Johnson 
in which the heated milk in bottles received a pri- 
mary cooling by means of blasts of air at ordinary 
temperatures. These experiments indicated that 
a considerable economical saving of cooling medium 
thus could be effected. Completing the cooling by 
means of blasts of chilled air produced satisfac- 
tory results. The fact that the cooling process 
required a long time seemed to produce no harm- 

86 



FROM THE PRACTICAL VIEWPOINT 

ful effects upon the milk. There was no noticeable 
increase in bacterial content when the cooling was 
accomplished within two hours. These results 
were obtained under conditions which somewhat 
approached what might be termed laboratory sur- 
roundings, and it is possible that under the stress 
of commercial conditions^ difficulties of operation 
might develop which would unfavorably influence 
the results. 

There is one objection which has been raised in 
the practice of pasteurization in the bottle which 
may have some weight in certain circumstances. 
It is claimed that because of the fact that the bot- 
tles are tightly sealed, there is no chance for the 
escape of disagreeable or offensive odors. In other 
heating and cooling processes, a certain amount of 
aeration takes place, with, as claimed by some 
dealers, beneficial results. Those who advocate 
bottle pasteurization claim that during the process 
of heating, the objectionable gases are driven out 
of the milk and are forced beneath the bottle cap 
into the outer air. In so far as known to the 
writer, the correctness of this claim has not been 
demonstrated. Neither is it known that objec- 
tionable odors or flavors have been subjects of 

87 



THE PASTEURIZATION OF MILK 

complaint among the users of milk pasteurized in 
the bottle. 

An objection which may be a serious one at 
times is this. If the bottle caps are not abso- 
lutely tight, as may occur when bottle necks are 
chipped or uneven, there is an opportunity for 
water to be drawn into the bottle. When the cooling 
is being carried on there is, of course, a partial 
vacuum produced in the space above the milk, and 
if in cooling the bottles are immersed in water, 
then the water might be drawn into the bottle. If 
the water were impure the danger becomes ap- 
parent. 

A certain advantage in the use of the bottle pas- 
teurizing process from a commercial point of view 
becomes apparent when only small amounts of 
milk are to be treated. If individual dairies are 
compelled by legal requirements to pasteurize the 
milk sold, it is a comparatively inexpensive mat- 
ter to equip for pasteurizing in the bottle. The 
only equipment necessary is a tank large enough 
to immerse the filled bottles; facilities for supply- 
ing hot water to the tank, and also for replacing 
the hot water with cold when the heating is ac- 
complished. Heat-recording devices are manu- 

88 



FROM THE PRACTICAL VIEWPOINT 

f actured for use in connection with bottle pasteuriz- 
ing. When this method is installed in small dairies 
there is saved the expense of installing heaters, 
holders, coolers, pumps and piping. Equally im- 
portant to the dairyman is the fact that the oper- 
ating expenses are less, since the amount of ma- 
chinery to be kept cleaned and in repair is almost 
nothing. 

A process of pasteurizing which, so far as known 
to the writer, has been but little employed, con- 
sists in making use of the vacuum pans which are 
commonly employed in the manufacture of con- 
densed milk. With certain changes, these can be 
used satisfactorily in pasteurizing milk. As usu- 
ally constructed, these vacuum pans are retort- 
shaped structures made of copper, and contain at 
the bottom two or three coils of copper pipe, into 
which live steam is admitted. When milk is con- 
densed, these hot pipes raise the milk to the de- 
sired temperature, and the natural water contained 
in the milk is drawn off in the form of steam by 
means of the vacuum pipe attached to the top of 
the pan. If these pans are used without change 
as pasteurizing tanks, it is probable that the live 
steam in the heating coils would have a tendency 

89 



THE PASTEURIZATION OF MILK 

to scorch the milk^ and it would be necessary to 
replace the steam by hot water, which should be 
rapidly pumped through the coils, the water being 
maintained at a uniform temperature in tanks out- 
side the condensing pan. The pans could be used 
also for holding the milk after it is heated for any 
desired length of time. 

In plants where seasonal conditions require that 
the milk be used for different purposes at different 
times of the year, such an arrangement would 
effect a saving of expense in equipment, and 
would thus aid in obtaining greater operating effi- 
ciency. 

From time to time attempts are made to bring 
forward some new process for treating milk de- 
signed to reduce the number of bacteria in milk 
by some agency other than heat. One of these is 
the treatment of milk by means of an electric cur- 
rent. In one electric process, the milk is allowed 
to flow from chamber to chamber through orifices 
of small diameter. While so flowing it is sub- 
jected to a strong alternating current of electricity. 
It is claimed that this current destroys the bac- 
teria contained in the milk through the shock to 
which they are subjected, and that the digestive 

90 



FROM THE PRACTICAL VIEWPOINT 

qualities of the milk are not impaired^ but are 
rather improved. 

It is, however, found necessary to heat the milk 
to about 130° before subjecting it to the electric 
current, and during electric treatment it attains a 
temperature of about 158°, due to the resistance 
of the milk to the electric discharge. It is an 
open question whether the destruction of bacterial 
life, which undoubtedly takes place, is due to the 
electric current or to the heat to which the milk is 
subjected. The results of tests made of the milk 
so treated indicate that the percentage of bacteria 
destroyed is high. If the effectiveness of the appa- 
ratus depends upon the heat generated during the 
process, it is probable the high percentage of bac- 
terial destruction is partially due to the fact that 
milk flows in such a small stream through the ma- 
chine. Every portion of it is thus uniformly 
heated to the maximum temperature, and even 
when milk is not held for any appreciable length 
of time, it has been found in laboratory tests that 
the bacteria are killed. As before stated, it is a 
fact that mechanical defects which exist in all ma- 
chinery render it difficult to maintain uniform tem- 
peratures. This makes the holding of hot milk a 

91 



THE PASTEURIZATION OF MILK 

necessary requirement in order to equalize tem- 
peratures. 

The ultra-violet rays have been suggested as a 
means of killing bacteria in milk, Since^ however, 
these rays have but little penetrating power, it has 
been found that the opaque character of milk pre- 
vents obtaining the good results which have re- 
sulted in the use of the ultra-violet rays in water 
purification. 

The ozone process, which will by oxidation de- 
stroy some forms of bacterial life, and which will 
destroy odors, aLso acts upon the constituent parts 
of milk and so changes them that it seems probable 
that ozone can never be satisfactorily substituted 
for the usual pasteurization process. 

An ingenious idea has been brought to the 
writer's attention by which it was proposed to de- 
stroy the bacteria by treatment in vacuum. It is 
well known that when persons work under abnor- 
mally high air pressure as in tunnel construction 
under rivers, etc., it is necessary for them to exer- 
cise the greatest care in coming out into the normal 
air pressure. The air, which under pressure is 
absorbed in the bodily tissues, suddenly expands 
when the abnormal pressure is relieved. The cells 

92 



FROM THE PRACTICAL VIEWPOINT 

of the body may be strained or broken. In such 
case the disease known as "the bends" results. It 
has been proposed that a machine might be so con- 
structed that an abnormal air pressure upon the 
milk could be suddenly released^ thus allowing the 
air within the germ bodies to quickly expand and 
so destroy them. No such system has been made 
commercially available. 



93 



CHAPTER III 



HOLDERS 



As previously stated, the New York City De- 
partment of Health was the pioneer among health 
authorities to require that milk, in order to be offi- 
cially considered to be pasteurized, must be held, 
after heating for a definite length of time. When 
this regulation was adopted no holding device was 
upon the market which was suitable to be used on 
a commercial basis. Since that time most of the 
manufacturing firms making milk-handling ma- 
chinery have constructed and placed upon the mar- 
ket one or more forms of holding apparatus. These 
differ in detail, and to a considerable extent in the 
efficiency with which they operate. In general, 
however, it may be said they are naturally divided 
into two classes: 

First, those which may be termed absolute 
holders, and 

Second, those which are of the continuous or 
flow type. 

Absolute Holders 

The absolute holders are so called for the rea- 
son that the milk, after being heated, is all held 

94 



FROM THE PRACTICAL VIEWPOINT 

in tanks or compartments for a definite length of 
time before being discharged. 

The first holder placed upon the market was of 
this character, and consisted of an upright cylin- 
drical tank having partitions radiating from the 
centre, thus dividing the tank into eight compart- 
ments. Such a holding apparatus is illustrated in 
Fig. 20. The drawing, however, shows a later 
type of the same apparatus, in which there are 
eight separate tanks which are arranged in a cir- 
cle. An upright shaft extends through the centre 
of the tank or the group of tanks, as the case 
may be, to which is attached, at the upper end, a 
revolving spout, into which the milk is discharged 
through the pipe from the heater. This spout as 
it revolves causes each tank to be filled in turn. 
To each tank is attached at the bottom an outlet 
pipe and valve. These valves are kept closed by 
springs, and are opened by means of a revolving 
arm, or cam, attached to the lower end of the up- 
right shaft before referred to. These outlet pipes 
discharge into a common pipe, through which the 
milk is conveyed to the cooler. By placing the 
revolving inlet spout in proper position with rela- 
tion to the revolving cam at the bottom, it can be 

95 



THE PASTEURIZATION OF MILK 

readily seen that each tank will be emptied after 
the milk has been held in the tank during the time 
required for the shaft to make a complete revolu- 
tion. By properly gearing the mechanism which 
operates the shaft it can be seen that the time of 
holding can be fixed at will for any period de- 
sired. A little thought, however, will make it clear 
that the actual holding time will not equal the time 
required for the shaft to make a complete revolu- 
tion, since approximately one-eighth of this time 
is occupied in filling each tank, and one-eighth is 
required to discharge each tank. In order to ar- 
rive at the actual minimum time for which we can 
be sure all the milk is held, we must reduce the 
time of revolution by one-fourth, or 25 per cent. 
Thus if it is desired to hold the milk for thirty 
minutes, it is necessary that the time of revolution 
of the operating shaft be forty minutes, which 
reduced by 25 per cent, equals thirty minutes, the 
actual holding time. 

It is also necessary to make sure that the dis- 
charge pipes are completely closed before the milk is 
allowed to enter through the inlet pipe into any tank. 
Otherwise some milk may pass out of the holder 
without being held for any definite length of time. 

96 



FROM THE PRACTICAL VIEWPOINT 




97 



THE PASTEURIZATION OF MILK 



Another point to be observed when partitions 
separate tlie tanks is to make sure that no tank 
becomes filled to overflowing. In such case, the 
milk will flow into a tank from which milk is be- 
ing discharged, and thus the holding time becomes 
a matter of great uncertainty. 

In this form of holder considerable foam de- 
velops, due to the dropping of the milk for a con- 
siderable distance from the discharge pipe into 
the body of milk in the tanks. The foamy milk 
does not retain the heat as well as is desirable, 
and as a consequence the destruction of the bac- 
teria is not always sufficiently complete. 

In Fig. 21 the eight compartments or wells are 
themselves immersed in a tank of water, the tem- 
perature of which is kept somewhat above that to 
which the milk is heated. In this form of appa- 
ratus the tendency to foam is largely overcome 
from the arrangement which allows the milk to 
enter the well from the bottom. Both the inlet 
pipe and the outlet pipe are operated by means of 
mechanism, which is above the tanks. There are 
sixteen valves, each of which is made tight by a 
ground seat, upon which the valve sets. These 
valves are at the lower end of the plug shanks, 

98 



FROM THE PRACTICAL VIEWPOINT 




99 



THE PASTEURIZATION OF MILK 



which extend through the milk to the top of the 
tanks. Any loosening of these valves, or any in- 
accurate adjustment of the cams which operate 
them, may cause milk to be discharged from a tank 
before it has been held a proper length of time. 
The efficiency of the apparatus would thus be 
impaired. 

The fact that the temperature of the heated 
milk is not reduced during the holding process 
appears to be an advantage. The surrounding 
jacket of hot water maintains or increases the 
temperature of the milk in the vats. 

In Fig. 22 the eight tanks are arranged in a 
circle upon a frame or platform, which itself re- 
volves, carrying the tanks with it. A central tank, 
which is stationary, receives the milk from the 
heater. From this tank the milk is distributed to 
the various holding tanks by means of pipes, 
which radiate from a central valve beneath the re- 
ceiving tank. This single central valve is of very 
ingenious construction, and is so made that all the 
holding tanks are filled and are also discharged 
through the same valve. Thus it is seen that this 
one valve replaces the sixteen valves which are 
employed in such an apparatus as shown in Fig. 

100 



FROM THE PRACTICAL VIEWPOINT 




101 



THE PASTEURIZATION OF MILK 




Fig. 22-B 



21. The chances of valve difficulties are thus 
reduced. 

The arrangement of this valve is rather diffi- 
cult to describe. It is shown in Fig. 22-B. A 
central core is attached to the pipe, which de- 
scends into it from the central tank. This core 
remains stationary, and is provided with a sin- 
gle opening, which is a continuation of and is at 
right angles to the discharge pipe from the tank 

102 



FROM THE PRACTICAL VIEWPOINT 

above it. Outside this core, and closely fitting 
it, is a shell which revolves around it. Into this 
shell the eight pipes from the various holding 
tanks are fastened, and they are so placed that as 
the shell revolves each pipe is in turn brought op- 
posite to the opening into the inner core. The 
milk is thus admitted to the bottom of each hold- 
ing tank in turn. As the shell continues to re- 
volve each pipe in the outer shell passes in turn the 
inner opening and the milk supply is thus shut off 
from each particular tank, and so remains until the 
shell has nearly completed its revolution. The pipe 
opening from the holding tank then comes oppo- 
site to another opening in the inner core, which 
extends only a short distance into the core. This 
opening turns downward and is connected with a 
pipe, which discharges the milk to the cooler. Thus 
it is seen that each tank is filled in turn and is in 
turn discharged automatically. The same method 
must be employed for arriving at the minimum 
holding time as that used with the device illus- 
trated in Fig. 20, namely, the time of revolution 
must be reduced by 25 per cent. 

The exact holding time may be arrived at in 
another way, namely, by carefully noting the 

103 



THE PASTEURIZATION OF MILK 

exact time at which the last milk enters any sin- 
gle compartment of the holder, and then observ- 
ing the exact time at which the first milk flows 
from the same tank. The difference indicates the 
minimum holding time. Of course, some of the 
milk is held for a longer time than that which is 
thus indicated, but we are sure that none is held 
for a less time. 

It will be found that the time as observed in 
this way is nearly equal to that which we obtain 
by calculation, allowances being made for varia- 
tions in the mechanical exactness with which the 
machine operates. 

It will be seen from the illustration that the 
various holding tanks are insulated by a cork 
jacket, so that little heat is lost during the hold- 
ing period. It will be noted, however, that the 
pipes leading from the holding tanks to the cen- 
tral valve are not insulated, and in this condition 
the milk which lies in these pipes during the time 
of revolution may, and probably will, become 
cooled, and the effectiveness of the bacterial de- 
struction will be impaired. This having been 
brought to the attention of the manufacturers, they 
provided insulating jackets for the pipes as well 

104. 



FROM THE PRACTICAL VIEWPOINT 

as for the tanks. Discharge pipes constructed with 
these insulating jackets are now provided for ma- 
chines which are placed upon the market at the 
present time. 

A modification of this type of holder is now be- 
ing manufactured in which the holding tanks do 
not revolve but are made stationary and, instead, the 
central valve revolves. The same effect is secured 
as in the other type, and there is this advantage, 
that less power is required, and the heavy frame 
required to hold the revolving tanks is not neces- 
sary. There is also this added advantage, namely, 
that a small plant may install such an apparatus 
with but two or four tanks, and as business ex- 
pands there may be added other tanks, it being 
only necessary to change the shell of the valve 
which revolves about the core. 

In Fig. 28 there are seven oblong enamel-lined 
tanks which are immersed in a tank of hot water. 
These are each filled in turn by means of valves 
in a pipe which extends along the upper side of 
the series. These valves are opened and closed 
by means of an automatic arrangement operated 
by a revolving shaft extending parallel to the inlet 
pipe. A similar shaft extends along the discharge 

105 



THE PASTEURIZATION OF MILK 

pipe at the bottom of the series, and operates 
valves which automatically regulate the discharge 
of the milk. 

There is one thing which should be carefully ob- 
served regarding this form of holder. It will be 
noted that the two shafts which operate both the 
inlet valves and the outlet valves are impelled by 
a single worm-driven gear. Thus both shafts 
move in unison. Care must be taken to make sure 
that no inlet valve is opened into any tank till the 
outlet valve is completely closed, otherwise some 
milk will flow out without being held for the 
proper length of time. 

In calculating the holding time with this appa- 
ratus, it must be noted that since there are but 
seven tanks in the series, there is required one- 
seventh of the entire period of sequence for each 
tank to fill and one-seventh for it to be emptied. 
Thus the entire time of sequence must be reduced 
by two-sevenths. A little thought will make it 
clear that as the number of tanks in a series de- 
creases in number, the time of revolution or se- 
quence must be increased. With eight tanks a 
period of revolution of forty minutes reduced by 
25 per cent, would equal thirty minutes. If, how- 

106 



FROM THE PRACTICAL VIEWPOINT 




©I 



107 



THE PASTEURIZATION OF MILK 

ever, a seven-tank holder has a forty-minute se- 
quence, which is reduced by two-sevenths, we have 
a holding time of but twenty-eight and four- 
sevenths minutes, and so on as the number of 
tanks decreases. 

A modification of the valve system, shown in 
Fig. 23, is now provided by the manufacturers of 
this machine. A valve exactly similar in principle 
to that shown in Fig. 22-B is made use of. All 
tanks fill and empty from the bottom, thus avoid- 
ing foam and reduring the danger of by-passing 
the milk. 

All the types of holders already described are 
being used with very satisfactory results. To 
summarize the points which should be observed 
in either buying or supervising the operation of 
holders of this character: 

First. — Any serious loss of heat should be pre- 
vented by complete insulation of all tanks and 
pipes in which the heated milk is held. Of 
these insulations, the hot-water jacket is the most 
expensive and perhaps the best. There is a 
question whether the added expense secures 
enough added efficiency to render the expenditure 
wise. 

108 



FROM THE PRACTICAL VIEWPOINT 

Second. — We should be sure that every particle 
of milk is held for the minimum time required. 

Third. — The valves for admitting and releasing 
the milk must be so tightly fitted that no milk 
can by any possibility be discharged before the 
proper holding time is completed. It may be pos- 
sible for valves to become so worn by use that 
annular grooves will be worn around them, thus 
allowing milk to be by-passed while the valve is 
closed. 

Fourth. — Make proper calculation to determine 
that the cycle of filling, holding and emptying of 
the tanks is long enough to make sure that the hold- 
ing time is sufficient and in addition to allow for 
the filling and emptying of the tanks. 

Fifth. — Make sure that the inlet valve is never 
open into a tank before the outlet pipe is closed. 

Sixth. — Since the ease and convenience of clean- 
ing is an item of importance, as a general propo- 
sition it may be said that, other things being equal, 
a machine which has the fewest pipes and valves 
consistent with efficient operation is the most de- 
sirable. 

Seventh. — It is desirable that as little foam as 
possible be produced in the operation of a holder. 

109 



THE PASTEURIZATION OF MILK 

Whatever form of tank holder is used, it is nec- 
essary that it be thoroughly sterilized before use 
each day, by the admission of live steam for a 
considerable period of time. This sterilization is 
of importance not alone for the destruction of the 
bacteria contained in it, but also in order that the 
pipes and tanks may become thoroughly heated im- 
mediately before use. If they are not so heated, 
it will be found that the milk first admitted to the 
apparatus will be considerably cooled, and will be 
discharged at a temperature much below that re- 
quired by the regulations, and will so continue until 
the hot milk has itself slowly heated the appa- 
ratus. This may require fifteen or twenty minutes. 
It will be found under such circumstances that the 
milk first discharged from a holder contains many 
more bacteria than that which flows from it after 
the machine is heated. 

Another form of holder which belongs to the ab- 
solute type is that which is represented by the tank 
heaters shown in Figs. 11, 12, 13, 14, 14.-B, 15, 1 6, 
and previously described. In these the milk, after 
having been heated, is allowed to remain for any 
desired length of time, and is then released. This 
method of holding has produced very satisfactory 

110 



FROM THE PRACTICAL VIEWPOINT 

results. It has this advantage; that the milk 
comes in contact with no new metal or apparatus 
between the completion of the heating process and 
the time when the milk is cooled. One disadvan- 
tage is that since it requires considerable time for 
a large tank full of milk to be discharged^ the last 
milk leaving the tank is held for a period consid- 
erably longer than that which first flows from it, 
and this long holding tends to interfere with the 
proper rising of the cream. 

Continuous Holders 

The continuous or flow type holders differ from 
the absolute holders in that the milk, instead of 
being quietly held in retainers for a definite length 
of time until the required period for holding is 
completed, is simply retarded in its flow. This 
period of retardation is so extended that before the 
milk passes to the cooler it has retained its tem- 
perature for the length of time desired. 

There are several forms of continuous holders. 
One of the first of these is the so-called Park 
holder, invented by Dr. William H. Park, of the 
New York City Department of Health, and pat- 
Ill 



THE PASTEURIZATION OF MILK 




Fig. 24 



ented and given to the milk trade for use by the 
inventor. It is shown in Fig. 24^ and consists 
primarily of an upright cylindrical tank, into 

112 



FROM THE PRACTICAL VIEWPOINT 

which the milk flows at the top, and from which 
it is discharged at the bottom. An inverted goose- 
neck attached to the outlet pipe so directs the out- 
flow that no milk can be discharged until the tank 
has become filled. In theory, the hot milk which 
enters at the top becomes gradually cooled as it 
flows downward, and so the last milk to enter the 
tank will be the last milk to leave it. If this 
were entirely true, then the time required for fill- 
ing a tank would be identical with the holding 
time. In such case the various particles of milk 
would pass through the tank like a flock of sheep, 
one after another. Unfortunately, there are several 
disturbing elements which enter into the problem, 
and the particles of milk, instead of resembling 
sheep, more nearly resemble a flock of chickens 
in their behavior. In the first place, the milk 
which is nearest to the outside circumference of 
the tank becomes cooled more than that which is 
in the centre, and as it cools it increases in weight, 
and naturally falls to the bottom and goes out. 
This tendency is partly overcome by providing in- 
sulating jackets. In some cases, as in Fig. 25, 
the jacket is a hot-water covering contained in 
the space between the inner and the outer shell. 

113 



THE PASTEURIZATION OF MILK 

Again, it can be seen that if the temperature of 
the milk as it enters the tank from the heater is 
not accurately controlled, it will frequently occur 
that the temperature will drop, and this cooler milk 
will fall through the body of milk toward the bot- 
tom. It is also true that the force of the milk as 
it enters the tank from the heater will, unless this 
force is broken, tend to carry the milk deeply into 
the body of that already in the tank, and so cre- 
ate currents which will interfere with the actual 
holding time. This force is broken by placing 
some sort of a baffle plate under the inlet pipe. 
This baffle is sometimes so arranged that it floats 
on the surface of the milk, and rises as the tank 
becomes filled. In other cases a flat piece of 
metal is placed near the top of the tank, and may 
or may not contain perforations which allow the 
milk to flow through as well as over the edge of 
the plate. It is immaterial what form of spreader 
is used so long as the currents are broken up. It 
will be seen by referring to the illustration that 
the inverted U-shaped pipe for the discharge of 
the milk is provided with a by-pass valve, so that 
the tank can be emptied when the operation is 
completed for the day. It is important that this 

114 



FROM THE PRACTICAL VIEWPOINT 

U-pipe be provided with a vent at the upper end, 
otherwise a syphon will be created and the milk 
will all be rapidly drained from the tank. 

In plants where a large amount of milk is pas- 
teurized, and there is therefore a rapid flow, it is 
necessary to install more than one of these tanks 
in series, and in some instances three and four 
tanks are so installed, each succeeding tank being 
a little lower than the one before it, and the valves 
so arranged that the milk-flow is from one to the 
other through the entire series. This also helps 
to equalize any uneven temperature which may oc- 
cur as the milk is discharged into the first tank. 

With all these precautions to insure a steady 
and even flow, it is never safe to assume that the 
holding time is correct unless a test is made. Only 
two feasable means of so testing the tanks have 
developed. One is the color test and the other 
the temperature test. Neither are absolutely ac- 
curate, but are sufficiently so for practical pur- 
poses. 

In the color test, the tanks are filled with water, 
heated to the same temperature as is the case when 
milk is pasteurized. The time of filling having 
been observed, a solution of some intense color, 

115 



THE PASTEURIZATION OF MILK 

preferably methylene blue or uranin^ is allowed 
to flow into the tank with the heated water. The 
time is observed between the time of its introduc- 
tion and the time when the first trace of it appears 
at the outlet. In order to make the test as ac- 
curate as possible, care should be taken that a com- 
plete solution is made of the color, otherwise small 
particles of solid color may fall through the liquid 
and deceive the observer. The solution of any 
color is of course slightly heavier than the liquid 
in which it is dissolved, and the tendency is for 
it to fall after its introduction. Therefore, the 
solution should be made as nearly as possible of 
the same specific gravity as the water in the tank. 
If it can be made slightly less in weight than the 
water the result of the test will be rather better. 
Even with the greatest care, it seldom happens that 
two tests of the same apparatus will bring iden- 
tical results. Unless the speed of flow is accu- 
rately gauged, the results will differ. 

The temperature test is sometimes used to de- 
termine the efficiency of these holders. When this 
method of testing is employed it is the practice to 
fill the holders with water in the same manner as 
with the color test. The temperature of the water 

116 



FROM THE PRACTICAL VIEWPOINT 

as it leaves the heater is then suddenly raised 
5° to 10°, and the time at which the rise takes 
place is noted. A careful watch is then kept at the 
outlet of the holder to determine when any rise in 
temperature occurs at this point. The elapsed time 
indicates the time of holding. The temperature, 
instead of being raised, may be lowered a given 
amount at the heater, and the corresponding drop 
in temperature at the outlet noted. 

The inaccuracy of this method of testing is due 
to the fact that during the long holding period 
there is a natural tendency for the changed tem- 
perature to become diffused throughout the sur- 
rounding liquid. It can also be seen that when 
the temperature is raised the natural tendency is 
for the hotter liquid to remain on top of the tank, 
while if the temperature is dropped, the tendency 
is for the cooler liquid to settle toward the bot- 
tom of the tank. A graphic chart can be made 
showing the result of these tests very clearly. 
Using the upright gradations of the chart to indi- 
cate changes in temperature, and the horizontal 
gradations to indicate periods of time, the sudden 
rise at the heater will be clearly shown by an al- 
most perpendicular line. The line showing the 

117 



THE PASTEURIZATION OF MILK 

rise of temperture at the outlet will be compara- 
tively gradual in its rise and will not reach its 
highest point for a considerable time. It will also 
be found that the proportional rise in temperature 
at the outlet will not be as great as at the inlet 
of the holder. When the temperature of the inlet 
is dropped instead of being raised, it will be found 
that the change of temperature at the outlet occurs 
in a much shorter space of time. 

In choosing between the color test and the tem- 
perature test, it can safely be said that for the 
Park holder the color test is the more accurate. 
When the tubular holder is used, which will be de- 
scribed later, it is probable that the two tests are 
nearly equal in accurac}^ 

When two or more tanks are employed in series, 
it is desirable that the piping be so arranged that 
the lowest tank can be filled with milk first when 
the process of pasteurizing is commenced for the 
day, and then when the lower tank is full the up- 
per tanks should be filled and the process contin- 
ued in this manner. The milk will then flow 
through all the tanks in succession from the high- 
est to the lowest. The reason for filling the lower 
tank first is as follows: When each tank is first 

118 



FROM THE PRACTICAL VIEWPOINT 

filled, the milk of course falls from the inlet pipe 
at the top to the bottom of the tank, and afterward 
onto the surface of the body of milk in the tank as 
it fills up to the level of the outlet pipe. In conse- 
quence there is considerable agitation of the liquid 
and currents are created. This may cause the last 
milk which enters the tank to be the first to be 
discharged, and our holding time becomes a mat- 
ter of uncertainty. If, however, the lower tank is 
the first one filled, we are then sure that all the 
milk in this tank is held for at least the time re- 
quired for the other tanks to fill. 

This method of filling may be effected in either 
of two ways: First, a pipe may extend along the 
top of the tanks in such a way that by opening the 
proper valves the milk may be directed into either 
tank at will. Second, the pipe may be arranged 
at the bottom of the series in such a way that 
either tank may be filled, if the proper valves are 
opened and closed. Both arrangements of pipes 
are shown in Fig. 24. 

It has been found by tests that this form of 
holder never holds the milk for a period of time 
as long as that which is required for them to be 
filled. Depending upon the form of the tanks and 

119 



THE PASTEURIZATION OF MILK 

the method of construction, the percentage of hold- 
ing time to filling time is from 25 per cent, to 70 
per cent. It is usual to estimate the time as 60 per 
cent, of the filling time. It is true that tanks which 
are tall and of comparatively narrow diameter are 
more efficient than are short and wide tanks, the 
reason probably being that with long, narrow tanks 
the movement of milk is comparatively rapid, and 
there is less diffusion of the milk than when the 
movement is slow, as in the wide, short tank. Tests 
have been made which indicate that when the rate 
of flow is twelve feet or over a minute, there is 
very little diffusion of the liquid. 

In all tanks of this character it is desirable, and 
indeed almost a necessity, that some sort of an 
insulating jacket be provided in order that there 
be as little loss of temperature as possible during 
the holding process. The reason for this, as be- 
fore stated, is that the cooling of the milk which 
is near the outer circumference of the tank causes 
downward currents. Thus the milk which falls 
to the bottom on account of these currents is car- 
ried out of the tank before it has been held for the 
proper length of time. 

The insulation may be provided by means of 

120 



FROM THE PRACTICAL VIEWPOINT 

jackets of asbestos, cork or felt, or a surround- 
ing tank of water may be provided, as in Fig. 25. 
By means of the insulation, if properly applied, 
the heat will be retained and the milk as it flows 
from the tank will have a temperature but little 
below that at which it enters. When the hot water 
insulation is used, as in Fig. 25, the initial tem- 
perature of the milk may become somewhat in- 
creased during the holding period. This addi- 
tional heating, it can be seen, has a tendency 
to cause the milk which may enter the tank below 
the average temperature to become heated and rise 
toward the top of the tank, thus increasing the 
time for which it is held. As a matter of fact, the 
water-insulated tanks have shown a good percent- 
age of holding time as compared with the filling 
time when the color test has been applied. The 
test of their efficiency as measured by the destruc- 
tion of the bacteria contained in the milk is also 
good. 

This Park type of holding tank has been some- 
what modified by various manufacturers in this re- 
spect, namely, by introducing the milk at the bot- 
tom and allowing it to flow out at the top instead 
by the reverse method of flow. When the inlet 

121 



THE PASTEURIZATION OF MILK 

pipe from the heater enters the tank at the centre 
of the bottom, and the milk is forced upward till 
the tank is filled, the color tests made have indi- 
cated that their efficiency percentage was small. 
Especially was this true when the outlet pipe was 
at one side and near the top of the tank. It can 
be seen that the force which is necessary to impel 
the milk in at the bottom against the weight of 
the superimposed milk in the tanks must of neces- 
sity create currents. This will be more noticeable 
if the milk is forced through the heater by means 
of a pump. The impulses will create a somewhat 
uneven flow and the resulting currents will be 
greater. The discharge of the milk from one side 
of the top also tends to cause currents and an 
uneven overflow. 

One manufacturer has so constructed his tanks 
that the inlet pipe enters at the top through the 
cover, is carried down through the body of the 
milk in the tank to the bottom, and then dis- 
charges the milk into the tank by means of an 
enlarged perforated foot somewhat resembling a 
sprinkler head on a watering can. In the plants 
where this apparatus is used the milk flows by grav- 
ity and there are thus no pump impulses. The 

122 



FROM THE PRACTICAL VIEWPOINT 




Fig. 25 



force is broken up by the descent of the milk 
through the body of that in the tank. It can be 
seen that when the milk as it enters the tank is be- 
low the average temperature, the tendency will be 

123 



THE PASTEURIZATION OF MILK 

for it to remain at the bottom, and so be heated 
before it is discharged. In this holder, also, the 
outflow is from the top, but the flowage into the 
discharge pipe is from many points at the surface 
into a gathering pan. In this way surface cur- 
rents are avoided. 

One of the disadvantages of the upright tank 
holder is that when it is of large size it is rather 
difficult to clean. It becomes necessary for the 
workmen to get inside the tank in order to thor- 
oughly clean it. Some upright tanks are being 
made which are mounted upon trunions in such a 
way that when the pipes are disconnected the tank 
may be turned into a horizontal position, and the 
cleaning can then be more easily performed. 

A second form of continuous or flow type tank 
is so constructed that a long horizontal tank, which 
opens at the top, is divided by cross partitions into 
several compartments. At the top of each of these 
partitions is a gathering trough, extending along 
the upper edge of the partition. A tube attached 
to the centre of this trough extends to near the 
bottom of the next succeeding compartment. This 
is shown in Fig. 26. 

In operation, the milk enters into the compart- 

124 



FROM THE PRACTICAL VIEWPOINT 




Fig. 26 



merit at one end of the tank, and when the com- 
partment is full, the milk flows into the gathering 
trough and is carried by means of the tube to the 
bottom of the succeeding compartment. Here the 
same routine is repeated till all the compartments 
are full. Then the flow becomes continuous till 
all the milk is pasteurized. When all the milk has 
left the heater, of course the flow from the holder 
stops. The tanks are at this time all full, and 
it is then necessary to remove the plug which is 

125 



THE PASTEURIZATION OF MILK 

near the bottom of each compartment in turn 
till all are emptied. Since these plugs are re- 
moved by hand^ it is necessary to place the hand 
and arm into the empty compartment at each 
operation. The danger of contamination is thus 
evident. 

When the partitions are low it has been found 
that the milk flows over the tops of all of them, 
and there is thus but little holding time possible, 
since the milk flows almost directly from the inlet 
to the outlet pipe. Even with the best of con- 
struction, tests have shown that the percentage of 
holding time to the filling time is small, sometimes 
being as low as 10 per cent, to 15 per cent. 

The third form of continuous flow type holder 
now used quite extensively is shown in Fig. 27. It 
consists of a series of large-size tubes arranged in 
a box- like structure. These tubes are connected 
one with another at the ends by suitable hinged 
heads, so that the milk which enters the top tube 
of the series flows forward and backward through 
all of them and is discharged from the lower tube. 
The discharge pipe is carried upward in the form 
of an inverted U tube in a similar manner to that 
shown in Fig. 24. This gives assurance that no 

126 



FROM THE PRACTICAL VIEWPOINT 




127 



THE PASTEURIZATION OF MILK 

milk will be discharged until all the tubes have 
become filled. 

In this form of holder, the flow of milk through 
the apparatus is comparatively rapid. As before 
stated, this rapid flow tends to prevenjt diffusion, 
and the holding time more nearly approaches the 
time required to fill the apparatus than in any 
other form of flow-type holder. In some respects 
it is rather difficult to make a satisfactory color 
test upon this holder on account of the fact that 
the air, which of course fills the holder when the 
filling with milk is commenced, is not all forced 
out as completely as is desired, and thus air pock- 
ets are formed. It thus occurs that some milk is 
forced from the discharge tube before the appara- 
tus is completely filled. Thus it is difficult to ob- 
tain the exact time required to fill the tubes. It 
is claimed by the manufacturers that when it is 
operating under the most favorable conditions the 
milk will be held for 98 per cent, of the time re- 
quired for the apparatus to become filled. The 
tests observed by the writer indicate that the hold- 
ing time is from 80 per cent, to 90 per cent, of the 
filling time, which is a greater percentage than 
with other holders. 

128 



FROM THE PRACTICAL VIEWPOINT 

The same difficulty which is experienced in 
emptying the tubular heater is observed with rela- 
tion to the tubular holder. This is due to the very 
slight inclination or pitch of the tubes from the 
horizontal. In some cases it has been the prac- 
tice to force the last milk out of the tubes by fol- 
lowing it with water. The possibility of adul- 
terating the milk unless great care is exercised is 
apparent. In the later machines made, the tubes 
are given a greater pitch, and the objection due to 
slow drainage is at least reduced. 

It should be noted that unless the tubes are very 
thoroughly heated by means of hot water or steam 
immediately before use, the first milk entering the 
holder will be so cooled that its temperature at the 
discharge will be below that which is required. 

This form of holder can be easily cleaned, since 
the tubes are large, and can be readily opened. 
It is thus easy to force a suitable brush through 
the pipes, and it is not difficult to see if all dirt 
has been removed. It is of course necessary that 
the cleaning be performed with great thorough- 
ness in order that it be effective in the destruction 
of bacteria. 

Whatever form of holder is used, whether it be 

129 



THE PASTEURIZATION OF MILK 

of the absolute or the continuous type, careful 
sterilization should be practised, not only directly 
after the apparatus is washed each day, but also 
immediately before its use on the following day. 
The reason for this is due to the fact that any 
organic matter which may remain in the apparatus 
after wasliing may contain spores of bacteria 
which are not readily killed by the heating to 
which the apparatus is usually subjected. These 
spores may develop into active bacteria during the 
time that the apparatus remains idle. Especially 
would this be true if, as usually occurs, consid- 
erable moisture is allowed to remain in the machine. 
For this reason the holder should be thoroughly 
sterilized before use each day. It may here be 
noted that there is even a greater necessity for 
sterilizing the cooler, pipes, bottling machine, etc., 
with which the pasteurized milk comes in contact 
after leaving the holder. Any recontamination at 
these points is not afterward corrected and may 
be a source of danger. 

It should here be noted that a feature which 
has been introduced into some milk plants con- 
sists in a brief superheating of the milk after it 
leaves the holder. This is accomplished by allow- 

130 



FROM THE PRACTICAL VIEWPOINT 

ing the milk to flow in a thin layer over pipes 
which are heated to about l62° to l65°. The milk 
is then immediately cooled. It is claimed that bac- 
teria which are resistant to 142° temperature are 
nevertheless considerably weakened by this heat- 
ing, and are completely destroyed at the brief 
heating of 162°. It is also claimed that the cream 
rises in a more satisfactory manner when the ad- 
ditional heating is employed. The feature of ap- 
plying a brief superheating temperature to milk 
already pasteurized has been covered by a patent. 

It must be evident, when a little thought is 
given to the matter, that in order for any con- 
tinuous holder to be reliable, the rate of milk flow 
must be uniform. In very few forms of appara- 
tus is there any attempt to properly control the 
rate of flow. When milk flows by gravity, the 
rate at which it flows into the heater will depend 
partly upon the volume of the fluid in the tank 
which feeds the machine. When a pump is used 
to supply the heater, its rate of delivery may be 
influenced by the steam pressure, or by the degree 
to which the steam valve is opened, or by the con- 
dition of the valves and pistons. In places where 
a gravity flow is emjiloyed, it is not a difficult mat- 

131 



THE PASTEURIZATION OF MILK 

ter to arrange a feed cup which will make it cer- 
tain that no more than a definite amount of milk 
can reach the heater per hour. When a pump is 
used, a float valve in the tank which feeds the 
heater can be made to shut off the intake pipe to 
the feed tank. This increases the milk pressure 
upon the pump and the discharge pipe, and by 
means of a suitable valve this increased pressure 
is made to close the steam valve which supplies the 
pump. This method of controlling the flow of 
milk to the heater is in successful operation in 
several pasteurizing plants. 



132 



CHAPTER IV 

TEMPERATURE CONTROLLERS AND RECORDERS 

In order that uniformly good results in the pas- 
teurization of milk may be obtained, it is abso- 
lutely necessary that the temperature to which the 
milk is heated be controlled in such a way that 
there will be no great variation. In order to con- 
trol this properly, three things are necessary — 
first, a uniform, even flow of milk; second, a steam 
pressure which does not vary; and third, that the 
steam which is admitted to the heater be so con- 
trolled that whatever variations there may be in 
the temperature of the inflowing cold milk may be 
met by varying amounts of steam, admitted to the 
heater. This control will, of course, also prevent 
any excessive heating which would follow if too 
much steam entered the heating apparatus. 

The matter of an even milk flow has been dis- 
cussed in the previous chapter. 

The control of steam pressure may be accom- 
plished in various ways. It is, of course, necessary 
that there be sufficient boiler capacity to insure 
that the steam pressure does not fall below a cer- 

133 



THE PASTEURIZATION OF MILK 

tain minimum amount. One of the simplest meth- 
ods of steam pressure control is by an instrument 
constructed like the safety valve of a boiler. A 
movable weight upon an arm regulates the pressure 
which is desired. When properly set any increase 
of pressure above the desired amount lifts the arm 
and shuts the steam valve connecting with the pipe 
leading to the heater. Other more complicated 
forms of apparatus are on the market, the details 
of which it is not necessary to describe. 

In the matter of the control of the temperature 
at which the milk leaves the heater, it is, of course, 
possible to do this by hand. This method makes it 
necessary that a man constantly watch the ther- 
mometer attached to the outlet milk pipe, and at 
the same time open or close the steam valve to ad- 
just the steam flow to the varying temperature of 
the milk. 

If the speed of milk flow, and also the steam 
pressure is well controlled, it is possible for a care- 
ful workman to regulate the milk temperature with 
good success. If, however, these factors are con- 
stantly varying, it is nearly impossible for even a 
careful man to obtain good results. It is, of course, 
more economically eflficient to arrange for auto- 

134 



FROM THE PRACTICAL VIEWPOINT 

matic temperature control than to depend upon 
man power, provided, of course, that the machine 
works as it is intended to work. 

The machines designed to control temperatures 
are operated in two ways. In one machine the 
bulb which is inserted into the milk is filled with 
some volatile liquid like ether and is connected 
by means of a capillary tube with a pressure coil, 
which in turn regulates the flow of compressed air 
to a valve. The compressed air is employed as a 
motive power to operate the valve which regulates 
the admission of steam to the milk heater. Such a 
system involves the installation of an air pump 
and a tank for the storage of compressed air. To 
one unfamiliar with the apparatus the description 
may appear involved and the operation compli- 
cated. Fig. 28 shows this system. 

In another form of controller, electricity is em- 
ployed as a motive power in operating the steam 
valve instead of compressed air. The bulb which 
enters the milk contains two metals, which are so 
fastened together that the difference in expan- 
sion makes and breaks the electrical connection 
and the steam valve is operated by this means. 
This is shown in Fig. 29- This method can, of 

135 



THE PASTEURIZATION OF MILK 



a. 



> 
<. 

< 



or 
o 



CC 




136 



FROM THE PRACTICAL VIEWPOINT 



ELECTRICAL CONTROLEFJ 

RCCOROCF}^ 




To 
PAiTBURlZEft 




Terminal j 

To y^ 

controllino 

Valve 




Tlrminal To 
The-rmostat 




bcCTION OF 

Pastcurizer 



Fig. 29 



course, be employed only where an electric current 
is available. This current, however, may be fur- 
nished by a small inexpensive dynamo, which can 
be operated at any plant where power is available. 
Both these forms of control work in a satisfactory 
manner. Of course, they are somewhat delicate 

137 



THE PASTEURIZATION OF MILK 

in adjustment, and careful handling is necessary. 
Either form will control the milk temperature 
within 2°, as indicated by the temperature re- 
corder. 

A method of temperature control which was 
proposed by the writer some years ago had for its 
basis a principle which has been made use of 
in this connection to a limited extent only. This 
consisted in this, namely, that the temperature of 
the heating medium be so controlled as to remain 
constant, and that the milk which flowed out of 
the heater be kej^t at a uniform temperature by 
varying the speed of flow of the milk through 
the heater. This reverses or inverts the present 
practice, in which the speed of milk flow is con- 
stant, while the 'temperature of the heating med- 
ium varies. The proposed method would have 
this advantage, that no part of the milk could ever 
be heated higher than the temperature of the water, 
and if this water temperature were controlled by 
a thermostat no scorching of the milk would ever 
result. It is evident that with a uniform heating 
medium the milk which flows through the heater 
will take up more of this heat if the speed of flow 
is slow than it will if the milk moves rapidly over 

138 



FROM THE PRACTICAL VIEWPOINT 

tlie heating surface. A thermostat attached to the 
milk outlet pipe from the heater could be made 
to control the steam which supplied the milk 
pump. This would vary the speed of milk flow. 
If milk flows by gravity to the heater, the ther- 
mostat might be made to open or close a valve in 
the feed pipe. 

The nearest approach to the use of this prin- 
ciple occurs in some plants when the heated water 
is kept at a uniform temperature by a thermostat, 
and the milk flow is also constant. The heating 
surface of the heater is so very large compared to 
the amount of milk heated, that the water is never 
more than 3° or 4° hotter than the milk, and 
there is therefore no possibility of scorching the 
milk. In these plants also the efficiency of the re- 
generative principle is carried as near the theo- 
retical limit of perfection as it seems possible. The 
water leaving the heater is within a few degrees of 
the temperature of the cold milk entering the ma- 
chine. This cooled water is conveyed to the milk 
cooler, where it is used for cooling the hot milk. 
It becomes so heated when leaving the cooler that 
it is but a few degrees lower than the hot milk. 
It can be seen that but little steam is required to 

139 



THE PASTEURIZATION OF MILK 

again raise the temperature to the desired point. 
The increased amount of heating and cooling sur- 
faces required for this form of pasteurizing ma- 
chine calls for careful cleaning and sterilization. 

Automatic Recorders 

The automatic recording of the milk temperature 
is desirable, and in most cities where the pas- 
teurization of milk is subject to public control it 
is required. The milk company which is really 
anxious to put out a safe product wants an office 
record which will indicate whether the work is 
being properly performed. With health authori- 
ties, such a record is necessary, since it is impos- 
sible for inspectors to be at pasteurizing plants all 
of the time to watch their operations. A correct 
automatically made record is the best substitute 
for personal inspection. To be of ideal value, such 
a record should show, not only the temperature, but 
also the time of holding. When the tank or batch 
heater is used, the single recorder attached to the 
tank will show these items with fair accuracy, but 
the observer must note whether or not the cooling 
is either wholly or partially done in the tank itself. 

140 



FROM THE PRACTICAL VIEWPOINT 

If such cooling in the tank does take place, then 
the length of time for which the recording mark 
remains at the highest point is a correct indica- 
tion of the time for which the hot milk is held. 
If the cooling is performed entirely outside the 
holding tank, then allowance must be made for the 
time necessary for the milk as drawn from the 
tank to fall below the point where the thermome- 
ter bulb is inserted into the milk. It is plain that 
the making of the record by the recorder pen will 
continue as long as the bulb remains in the hot 
milk. Thus, if the highest temperature were re- 
corded for forty-five minutes, and it required twen- 
ty-five minutes for the milk in its discharge to fall 
below the recorder bulb, then the actual holding 
time for all of the milk would be but twenty 
minutes. 

When the continuous holding process is used, it 
is desirable that a recorder be attached to the out- 
let of the heater, and that another be placed in the 
outlet pipe from the holder. If the charts on these 
two recorders are both set at the correct hour of 
the day then it is easy to calculate the duration 
between the time of the first discharge of hot milk 
from the heater and the first discharge from the 

141 



THE PASTEURIZATION OF MILK 

holder. If one recorder only is in use^ it is more 
important that it be placed at the holder outlet. 
It is evident that if there is a serious loss of heat 
during the holding process due either to imper- 
fect insulation or to insufficient preliminary heating 
of the holder, then the milk would not be satisfac- 
torily pasteurized, since some of the dangerous 
organisms originally in the milk may escape de- 
struction. The holder recorder indicates this. 

The various recording instruments upon the 
market differ in this one particular, namely, that 
in one form ether, or a similar volatile fluid, is 
used in the thermometer bulb and capillary tube, 
while in the other, the bulb and tube are filled with 
mercury. One of the former is shown in Fig. 30, 
while the mercury bulb is shown in Fig. 31. There 
is a variation also in the method employed for 
regulating the recording arm. In a form of re- 
corder not shown, another form of adjusting screw 
is attached to the recording arm, and an improved 
device is used for securing the paper chart to the 
face of the instrument. 

In the selection of a recording instrument, one 
of the most important points to consider is its sen- 
sitiveness to rapid or frequent changes in tempera- 

142 



FROM THE PRACTICAL VIEWPOINT 



•'ink. ^ 

IS*"' 
58| 




•J ^ a a - " "^ 



o 

CO 



I 

!^ 111 




V vy "? 3 i 

'^ -C: .V t o o o 

t c a -^ S .\ H: 

2 S S c 6' 5 S 

"i CQQ g ^ :J O 






143 



THE PASTEURIZATION OF MILK 





Fig. 31 



ture. If it is slow in responding to such changes, 
there is a possibility that there may be a wide 
fluctuation of temperature, which will not be shown 
upon the recording chart. The manufacturer of 
each instrument claims that his machine is very 
sensitive to rapid temperature changes. 

It should be borne in mind that a temperature 

144< 



FROM THE PRACTICAL VIEWPOINT 

recorder is in reality a pressure recorder only in 
which the changes in pressure due to varying tem- 
peratures are so graduated as to indicate with 
fair accuracy the temperature of the milk. With 
the ether instrument, the amount of movement of 
the arm for, say, a ten degree rise, changes as the 
higher temperatures are reached. So the grad- 
uations on the chart are not of the same width all 
the way across. In the mercury instruments this 
is not true, but the degree graduation lines are 
equally distant one from the other. There are cer- 
tain inaccuracies in these instruments which must 
be taken into account. Thus it can be seen that 
the temperature of the room in which the recorder 
is placed must have an effect upon the pressure 
coil. In the instrument shown in Fig. 30 an at- 
tempt is made to correct this by attaching to the 
arm a compensating coil. This coil also contains 
mercury, and is so placed that it moves in a di- 
rection opposite to that of the coil to which the 
capillary tube is connected. The recording arm 
is attached to both coils. When, therefore, both 
coils move as the result of the room temperature, 
no effect is produced upon the recording arm, but 
it remains stationary. Any increased pressure in 

145 



THE PASTEURIZATION OF MILK 

one due to the temperature of the heated milk will 
move the pen and cause it to make a proper rec- 
ord. The same effect may be produced in another 
way. In this case the comjDensating coil is con- 
structed of two different metals, and the differences 
in expansion cause it to move, but in a direction 
opposite to that produced by the ether coil. 

It must also be borne in mind that the recorder 
does not register absolute temperatures, but only 
relative changes in temperature. Thus inaccurate 
adjustment of the arm may produce a record which 
is deceptive. For this reason it is necessary to 
provide some means of adjusting the arm in order 
to secure an accurate reading. In some instru- 
ments the arm has a flexible joint which can be 
moved by hand. This is rather difficult to accom- 
plish, without danger of breaking the recording 
arm, and fine adjustment is not easy. There is 
also the danger that the joint will be uninten- 
tionally moved when placing the chart upon the 
face of the dial. 

In one recorder a post is so placed that it can 
be turned by means of a clock key. After the 
proper adjustment has been made, the post may be 
held in proper position by sealing it to other rigid 

146 



FROM THE PRACTICAL VIEWPOINT 

posts beside it. This form is of value to the in- 
spector, since by placing his seal upon it he can 
be sure that no change is made in the recorder 
during his absence. 

In other instruments other means of adjustment 
are provided. If, as in some forms, the coil is so 
placed that its axis of rotation is the same as that 
of the recording arm, then no movement of the arm 
at the joint can affect the relative temperature 
valves of the varying degree spaces upon the chart. 
With this form there appears also to be less lia- 
bility to vibrate with the vibration of the walls of 
the buiding in which it is placed. This form also 
has the advantage that the knob or screw which 
holds the chart to the face of the dial is so ar- 
ranged that the chart cannot be left loose upon the 
apparatus, but must either be securely fastened 
or left off the instrument altogether. It is also 
very easy to fasten the chart to the clock face. 

It has frequently been found by inspectors that 
instruments were not accurately adjusted. This 
may be due to a defect in the instrument itself, or 
it may be due to an intentional false adjustment 
by the man who is operating the pasteurizer. He 
may wish to indicate upon the chart a higher tem- 

147 



THE PASTEURIZATION OF MILK 

perature than is actually employed in the pas- 
teurization of the milk. For this reason those in- 
struments whose adjustment is under the control 
of the inspector alone are desirable. They should 
be frequently tested. This frequent checking is of 
advantage to the honest milk dealer as well^ since 
if a recorder by any means shows a temperature 
lower than it should^ there may be trouble with 
the cream line due to an unsuspected high tem- 
perature in the pasteurizer. 

Health authorities must be alert in watching the 
temperature records which are kept on file by the 
dealer. It is, of course, possible for a dishonest 
dealer to make false records. These may be made 
in various ways. Instances have been known 
where the entire record has been made by hand, 
an ordinary pen being used. This requires more 
skill than the average dealer possesses, if he is to 
deceive the wideawake inspector. It is possible 
to put a chart upon a recorder dial and leave it so 
loosely attached that it does not revolve with the 
clock. Then, when the desired temperature is 
reached, the chart may be turned by hand and a 
beautiful even line be drawn upon it. When the 
first milk from a holder has a temperature lower 

148 



FROM THE PRACTICAL VIEWPOINT 

than required by law, some dealers wait until the 
proper temperature is attained, and then, by plac- 
ing the thermometer bulb in the milk, they get a 
record which indicates an immediate rise of tem- 
perature to the highest point, and then a uniformly 
even line. Any record which indicates that the 
temperature has been raised at once to the maxi- 
mum point, and then continues with no variation 
during the entire run, should be looked upon with 
suspicion. Inspectors with a little experience soon 
learn to detect false records, by evidences not al- 
ways easy to explain, and they are able to gain 
from dealers the admission of irregularities which 
are at first denied. 



149 



CHAPTER V 

CLEANING AND COOLING THE MILK CLEANING 

CONTAINERS HOME PASTEURIZATION, ETC. 

It is of course needless to say that all milk 
should be clean when it arrives at the plant where 
it is to be pasteurized. That is^ there should be no 
visible dirt in the milk. It is also desirable that 
all dirt which is not readily detected be absent. 
While visible dirt and bacteria are not identical, 
still it is true that visible dirt is almost always ac- 
companied by bacteria in large numbers. Dealers 
should therefore make every effort to induce the 
dairymen to be so cleanly in their methods that 
very little dirt will find entrance into the milk. 
The sediment test when properly used is an ex- 
cellent method of finding out whether or not the 
dairyman is cleanly in his methods. If, however, 
the producer is allowed to strain his milk before 
bringing it to the shipping station, then the sedi- 
ment test simply tells the dealer whether or not 
the farmer has strained the dirt out. Or rather, 
let us say it indicates either that the farmers' 
methods of caring for the milk are cleanly, or that 

150 



FROM THE PRACTICAL VIEWPOINT 

the evidence of his uncleanliness has been strained 
out. It seems wise to advise dealers to prohibit 
the straining of milk at the farm. This may 
seem like radical doctrine, but a little thought dis- 
closes its wisdom. If the milk is unstrained, then 
the sediment test becomes of real value to the 
dealer in directing his attention to those dairymen 
who need attention from the inspector. Then, 
again, after the dirt once gains access to the milk, 
the straining simply removes that part of the dirt 
which is the least objectionable, namely, the in- 
soluable part. If milk is poured over a strainer, 
the dirt remains upon the surface, and the milk 
which may be afterward poured through the 
strainer helps to carry through those soluble por- 
tions which may have at first escaped solution. 
This soluble portion, of course, contains most of 
the bacteria. 

The removal of the dirt at the shipping sta- 
tion or the pasteurizing plant may be accom- 
plished by straining as it is received, or since the 
straining of cold milk is difficult, it may be strained 
while hot from the heater and before it enters the 
holding apparatus. There is no objection to this, 
since whatever bacteria are carried through into 

151 



THE PASTEURIZATION OF MILK 

the holder are destroyed during the holding 
process. 

Clarification 

The centrifugal clarifier is used to a large ex- 
tent^ and removes not only the dirt which is ordi- 
narily seen in milk, but also the pus cells, blood 
cells, etc., which usually escape detection. The 
clarifier, as is well known, is made in a manner 
similar to a separator, the difference being that 
the cream is not separated from the milk, but the 
dirt, pus, etc., is thrown against the outer por- 
tions of the revolving shell, and is there collected. 
Of course, this material contains a great many bac- 
teria, which are carried along with the heavier ma- 
terial. Tests, however, made by the plating 
method, do not show the great decrease in the 
number of bacteria which might be expected, and 
in many instances the apparent number is in- 
creased. This is probably due to the fact that the 
clumps of bacteria are broken up and so produce 
more colonies upon the plate than results when 
they remain bunched together in the original milk. 
One of the clarifiers is illustrated in Fig. 32. 

One objection to the clarifier has been the 

152 



FROM THE PRACTICAL VIEWPOINT 




THE PASTEURIZATION OF MILK 

tendency which there was to create foam^ espe- 
cially if the milk were cold. This foaming is due^ 
of course_, to the entrance of air into the milk dur- 
ing the process. Milk which has been previously 
pumped seems more likely to foam than when 
pumps have not been used. Machines are now 
made by which the air is excluded, and no foam, 
or almost none, is produced when they are oper- 
ated, even when the milk is cold. It is generally 
held that the clarification of milk by a centrifugal 
machine is a good thing. It is claimed that the 
pus cells, leucocytes, etc., which are in the milk, 
tend to form a covering for the bacteria contained 
in the milk, to such an extent that they are some- 
what protected and are not so readily destroyed 
by heat. It is claimed that the removal of this 
covering by means of the clarifier therefore assists 
in the complete destruction of the bacteria. This 
claim has not been fully demonstrated to the knowl- 
edge of the writer. 

It is the practice of some dealers to strain the 
pasteuried milk as it enters the bottling machine. 
This is to be condemned unless the strainer is 
completely covered and is sterilized at the same 
time that the final sterilizing of the bottler occurs. 

154 



FROM THE PRACTICAL VIEWPOINT 

In fact_, any straining after the milk leaves the 
holding apparatus is undesirable, and seems to be 
useless if the milk has been well cleaned before 
pasteurizing. 

Coolers 

The rapid cooling of heated milk has been held 
to be an important factor in the satisfactory pas- 
teurizing of milk. It was claimed that the sud- 
den chilling had a destructive effect upon the bac- 
teria_, which had been already weakened by the 
heating. Investigations made by Ayers and John- 
son, however, seem to indicate that when the cool- 
ing is accomplished, during a period of two hours, 
there is no noticeable increase in bacterial growth. 

There are three general types of milk coolers 
in use: 

First; The open cooler or aerator. This consists 
of a series of tubes, made usually of copper and 
well tinned. These tubes are arranged one above 
another, and are so connected at the ends that cold 
water or brine is forced through the entire series. 
The water flow is into the lower tubes and up- 
ward through the series, so that the coldest water 
comes in contact with the coldest milk. This form 

155 



THE PASTEURIZATION OF MILK 




Fig. 33 



of cooler is shown in Fig. 33. The cooler is usu- 
ally arranged in sections. Through the upper 
section cold water, frequently well water, flows, 
while the lower section contains ice water or brine. 
This form of cooler is very effective in rapidly 

156 



FROM THE PRACTICAL VIEWPOINT 

cooling the milk when it is made large enough to 
take care of the milk which is to be treated. They 
are made by various manufacturers in forms which 
vary somewhat in details. Some are so arranged that 
the regenerative principle is made use of. In most 
of these the hot milk from the holder is allowed 
to flow over pipes through which the incoming 
cold milk flows. This is a means of saving heat 
units, but such coolers are rather difficult to clean, 
and there is a danger that the pressure of the cold 
milk on the inside of the pipes will find openings 
through which the milk will be forced into the pas- 
teurized milk on the outside. The contamination 
which results is not corrected by repasteurization. 
Some one may say that the same danger exists when 
the cooling medium on the inside of the pipes is 
water. This is true, but it must be remembered 
that the water pipes do not need to be taken apart 
for cleaning, while the milk pipes must of neces- 
sity be opened for cleaning daily, and the danger 
from loosened joints is therefore greater. 

Another objection which has been urged to the 
use of the open cooler is that the milk is exposed 
to the air, and that there is great danger from 
air contamination. This is true when the air is 

157 



THE PASTEURIZATION OF MILK 



full of dust or foul odors. In most milk plants^ 
however, the air is so moist that little dust is flying 
about, and recent investigations by Ruehle and 
Kulp * of milk contamination by stable air indi- 
cate that even under unfavorable conditions the air 
contamination is not as serious a matter as we have 
supposed. Of course, milk coolers can be en- 
closed by tightly fitting metal covers, or they may 
be located in separate rooms or compartments, and 
so be protected from contact with air which is 
questionable. If a separate room is provided, 
suitable ventilation should be secured for carrying 
off steam, and the opening for the admission of air 
should be so protected that the incoming air will 
be filtered. 

Since it is difficult to clean and sterilize metal 
covers for coolers, it seems more desirable that the 
milk be protected by enclosure in separate rooms. 

The complete sterilization of this open type of 
cooler is a rather difficult matter. The reason for 
this is that the cooling surface cannot be subjected 
to the action of steam under pressure. The usual 
method employed is to direct live steam from a 



*BuI. 409. N. Y. Agricul. Exp. Sta. 

158 



FROM THE PRACTICAL VIEWPOINT 

hose against the outer surface of the pipes, after 
the washing has been completed. It is well known 
that steam when relieved of its pressure rapidly 
cools, and a person can hold his hand a short 
distance from an open steam pipe with no incon- 
venience. It often happens that not all the parts 
of the cooler receive the benefit of even this re- 
duced temperature. The tubes, of course, must 
be empty of the water usually contained in them 
before they are steamed. 

It might be feasible to provide covers for these 
coolers which would be sufficiently tight to allow 
the pressure of the steam to be retained to some 
extent before it escaped into the outer air. Some 
covers are now made which are fairly tight. 

The best way to sterilize this form of cooler is 
to have the tubes of sufficient strength so that 
steam may be admitted on the inside under pres- 
sure. In such case the sterilization is from the 
inside. If, while the pipes are hot from the en- 
closed steam, water is allowed to trickle over the 
outside, this is heated, and is itself converted into 
steam, which helps to cleanse the pipes. 

Care should be taken to be assured that the 
steam which rises from the milk while being cooled 

159 



THE PASTEURIZATION OF MILK 

does not become condensed upon any unclean sur- 
face, such as the ceiling or a metal covering over 
the cooler, and from thence fall back into the milk. 
If this occurs, very serious contamination may 
result. 

Open pipe coolers should not be made very long 
in relation to their height. It can be seen that 
the water flowing through long pipes will become 
warmed on the inner surface of the tubes, while 
the central more rapidly flowing core may still be 
cool. More ejffective cooling is obtained where this 
milk flow is broken up by frequent turns as the 
water is returned from one pipe to another. 

Second: The cooling may be accomplished in 
the same apparatus in which the milk is heated 
and held. This can be done when the tank sys- 
tem of pasteurization is employed, as illustrated in 
Figs. 12, 13, 14, 1 i-B, 15, 16. When cooling is so 
carried on, the cold water or brine takes the place 
of the hot water in the pipes, by means of which 
the heating was originally done. It is found in 
practice that when the same coil is used for the 
brine as well as for the hot water, there is dan- 
ger that careless workmen may allow the brine and 
the water to become mixed. There is therefore a 

160 



FROM THE PRACTICAL VIEWPOINT 

loss of brine. Some heating tanks are now made 
with double coils^ one of which is used for heating 
and the other for cooling. If the cooling is done 
in tank pasteurizers there is the advantage that 
the milk comes in contact with no additional metal 
surface or other material after it is placed in the 
tank till it is drawn into the final containers. 

The principal objection to the tank cooling is 
that usually a long time is required to reach the 
desired low temperature. As stated in the chap- 
ter on heaters, the time is frequently from an hour 
to an hour and a half. Large coils and a rapid 
circulation of brine will decrease this cooling time 
greatly. 

In country plants at a distance from the point 
of milk consumption, the time of cooling is an im- 
portant consideration from the dealers' point of 
view, since the time between the receipt of the milk 
from the farmer and the departure of the milk 
train is limited. 

The change in temperature from the high heat 
necessary to pasteurize the milk to the cold re- 
quired for rapid cooling produces a considerable 
strain upon the pipes of the coils, and the joints 
are apt to become weakened. 

161 



THE PASTEURIZATION OF MILK 

Third: The tubular cooler is being used to a 
considerable extent. In this form of cooler the 
pipes through which the hot milk flow are en- 
closed by other pipes^ through which cold water 
is forced in a direction opposite to the flow of 
the milk. These coolers are exactly similar to 
the tubular heaters illustrated in Figs. 7, 10, 
and 11. 

This form of cooler is effective and rapid; it has 
this advantage, that sterilization by steam under 
pressure can be made complete. There is the same 
difficulty in emptying the tubes which was noted 
in describing the tubular heater and holder, and 
whatever advantage there may be in exposing milk 
to the air in order to get rid of bad odors, etc., is 
absent from the tubular cooler. 

The regenerative principle is made use of in the 
tubular heater and cooler, as already described, 
and there is little danger of the milk becoming 
contaminated by leakage of the water, since the 
joints of the water pipes do not come in contact 
with the joints of the milk jDipes. 

One of the most efficient forms of apparatus to 
use from the point of view of economy of heat 
units is probably that shown in Fig. 11. The 

162 



FROM THE PRACTICAL VIEWPOINT 

great amount of piping, however, renders it diffi- 
cult to keep clean. 

Washing of Containers 

It is of course important that containers in 
which pasteurized milk is placed shall be thor- 
oughly cleaned and sterilized. There can be little 
advantage gained in the proper pasteurization of 
milk if it is to be immediately placed in contain- 
ers which are not free from all dangerous bacteria. 
The relative importance which the cleaning of cans 
and bottles has in the bacterial content of milk 
has not been recognized to the extent which it 
deserves. 

Cracks and open seams, especially in milk cans, 
may harbor particles of milk which are heavily in- 
fected with bacteria, which in many cases are of a 
type which are difficult to destroy by ordinary 
methods. Especially is this true if the cans or 
covers contain moisture, since this aids in the de- 
velopment of the bacterial life. 

It is undoubtedly true that the methods em- 
ployed in washing bottles are generally much more 
satisfactory than those in use in handling the cans 
and covers. Bottle-washing machines of various 

163 



THE PASTEURIZATION OF MILK 

makes are on the market which perform excellent 
work. Some of these employ revolving brushes, 
which are automatically forced into the bottles, in 
which a strong washing solution has been placed. 
In others, the cleaning is accomplished by inject- 
ing under high pressure jets of washing solution 
into the inverted bottles. This type of machine is 
that which is in the most general use at the pres- 
ent time. 

As usually constructed, this washing apparatus 
is a long machine, in which are placed several 
tanks for containing the washing and rinsing 
fluids. One tank contains a strong washing solu- 
tion, another contains water for the first rinsing, 
and a third contains clean water for the final rinse. 
Over these tanks are placed plates having a sur- 
face area of about the same size as that of the top 
of a bottle case. These plates are perforated, and 
powerful pumps force the liquid in the tanks 
through these perforated plates in such a way that 
the liquid is forced upward into the bottles, which 
are inverted in cases over them. An automatic 
feed pushes the cases from plate to plate along a 
track made for the purpose. The bottles thus get 
first a cleaning with the fairly hot washing solu- 

164 



FROM THE PRACTICAL VIEWPOINT 

tion, then a rinsing with hot water, after which 
clean water is forced into them, which is near the 
boiling temperature, and sometimes a final jet of 
live steam is forced into the bottles. If the final 
rinse water is clean and hot, and the steam is ap- 
plied long enough, the bottles leave the machine 
at a temperature of from 150° to 170°, and are 
reasonably free from bacteria. 

Several points are to be borne in mind in using 
a machine of this kind. In the first place, no ma- 
chine can be depended upon to fully clean an 
extremely dirty bottle, particularly those which are 
returned from the bottle exchanges and the dumps. 
Such bottles should first be washed by hand upon 
revolving brushes, where they can be clearly seen 
by the workman. They should then be washed again 
in the regular jet- washing machine. Another im- 
portant point is that the perforations in the wash- 
ing plates are liable to become clogged either with 
particles of dirt, or with rust, or it may be with 
deposits which are thrown down from water which 
is very hard. If these openings are stopped up 
it will mean that some bottles are not washed as 
it is intended they should be, and dealers may be 
unable to account for an unusually large number 

165 



THE PASTEURIZATION OF MILK 

of dirty bottles which they find from time to time 
upon their routes. 

Another important item is the temperature of 
the rinsing water. Unless this temperature is con- 
trolled by a thermostat, it may be easy to care- 
lessly let the temperature drop below the steriliz- 
ing point. Workmen who have to take away the 
washed bottles from the machine and store them 
find that it is uncomfortable to handle bottles which 
are extremely hot, and these men may, therefore, 
allow the steam supply to the rinsing tank to be 
cut down to such an extent that the bottles do not 
get sterilized. A thermostat attached to this 
rinsing tank will automatically keep the tempera- 
ture up to the desired point. If, in addition to 
this, a temperature recorder is also attached to this 
tank, a record will be kept which a dealer may 
keep on file as an office record. This will enable 
him to keep in closer touch with the work which 
is being done in his washing-room. 

Another important matter is to make sure that 
the water which is used for the final rinse water 
is fresh, clean water, and that it is not used over 
and over in the final rinse tank. Most of the 
newer machines are so arranged that the water 

166 



FROM THE PRACTICAL VIEWPOINT 

which is forced into the bottles for the final rinse, 
instead of falling back into the tank from which 
it is pumped_, is carried back into the tank behind 
it. From here it can be properly used for the pre- 
liminary rinsing of the bottles. The use of fresh, 
clean water for final rinsing is somewhat expen- 
sive when a public water supply is used, and also 
a good deal of steam is required to heat it, but in 
order to obtain sterile bottles it is necessary. For 
heating this water use can be made of the exhaust 
steam from engines and pumps, and thus heating 
expenses may be cut down. 

There is one form of automatic washing ma- 
chine in which the bottles which are being treated 
are forced down into successive tanks of water, and 
the inverted bottles are pushed over fingers from 
which water is forced in a direction somewhat 
tangent to and also at right angles to the inserted 
finger. The water as it is forced into the bottle 
has therefore somewhat of a scouring action. This 
is of advantage in removing dirt which has ad- 
'hered to the glass. In this machine, also, the 
water which is used for the final rinse is heated 
under pressure, and as a result, when it is forced 
into the bottle, its temperature is frequently above 

167 



THE PASTEURIZATION OF MILK 

the boiling point. One feature of this machine 
is unique. The machine is so constructed that, 
when the final rinse water falls below a definite 
temperature, of say 180°, it refuses to operate, 
since the bottles will not be lifted from the rinse 
tank, but will remain submerged. The machine 
thus becomes its own thermostat. This effect is pro- 
duced in the following manner: The platform 
upon which the cases are placed, and by means of 
which they are lowered into and lifted from the 
rinsing tank, is so counterbalanced that when the 
bottles are full of water the weight is too great 
for the case to be lifted. If the water which is 
forced into the bottles is hot enough so that as re- 
leased from pressure it is converted into steam, 
then the water is forced out of the bottles, and they 
have sufficient buoyancy to enable the counter- 
weight to lift the entire case out of the tank. 

The older method used in washing bottles, even 
when large quantities were handled, was to pro- 
vide means for soaking the dirty bottles, then to 
wash them by hand on revolving brushes, and 
finally to sterilize them in separate rooms, or in 
tanks into which live steam was discharged for a 
considerable time. This method is still in use to 

168 



FROM THE PRACTICAL VIEWPOINT 



a considerable extent and is effective, but is more 
expensive than the machine method. This added 
expense is principally due to the amount of labor 
involved in the many handlings of the bottles 
which is necessary. Various soaking machines are 
in use. Some of them are so arranged that it is 
not necessary for the workmen to put their hands 
into the soaking solution, since an endless con- 
veyor carries the bottles into and out of the soak- 
ing tank. The solution is made so strong that all 
foreign matter, even the bottle caps, is disinte- 
grated. After being removed from the soaker, a 
rinsing by means of a machine which forces hot 
water into them renders them sterile. 

Some method of thorough hand washing with 
subsequent careful sterilizing probably gives bet- 
ter results than does machine work, provided the 
men who do the washing are careful to see that no 
dirty bottles get by them. This is an expensive 
method of cleaning bottles. 

Whatever method of washing is employed, care- 
ful attention should be given to proper inspection 
of the washed bottles. Probably no one thing can 
do more harm to a milkman's business than for his 
customers to frequently find bottles which have 

169 



THE PASTEURIZATION OF MILK 

dirt adhering to the inside of them. Even though 
the dirt may have been sterilized by the steam 
treatment and be therefore harmless, the custom- 
er's sense of cleanliness is offended and the dealer 
may lose his trade. 

A practice which has been adopted by some 
dealers commends itself to the careful milkman. 
This is the practice of restirilizing the bottles after 
they have been inspected and all dirty ones re- 
moved. Any contamination which may have re- 
sulted from the handling of the bottles by the 
workmen will thus be remedied. 

After treatment, washed bottles should be stored 
either in an inverted position until they are used, 
or else they should be protected by suitable cov- 
ers or by placing them in separate rooms where no 
infection can occur. If a cold-storage room is 
provided, for the washed bottles, there is a cer- 
tain advantage. When it is remembered that the 
mass of glass in a milk bottle nearly equals the 
mass of the milk contained in it, it can be seen 
that if the bottle is warm, before it is filled, the 
temperature of the milk will be raised to a con- 
siderable extent. When empty bottles are stored 
at room temperature in the summer, they may 

170 



FROM THE PRACTICAL VIEWPOINT 

have a temperature of 65° to 70° when the milk 
goes into them. If milk is cooled by the cooler 
no lower than 50°, it will, by coming in contact 
with the warm bottle, be warmed to a temperature 
of from 55° to 60°. Bacteria troubles may fol- 
low, especially if the cases of bottled milk are not 
immediately iced, or if they are placed in a cold 
room without ice being placed in contact with the 
bottles. 

It is a known fact that milk either in cans or 
bottles will be very slow in cooling if the con- 
tainers are placed in dry air, even though the tem- 
perature of the air is considerably below that of 
the milk. Milk containers, however, which have 
ice placed upon them, will become cooled in a short 
time. 

Dealers and others have not realized to what an 
extent unclean cans and covers may, and in fact 
do, ajffect the bacterial content of the milk. Un- 
til comparatively recently, no effective can wash- 
ing, sterilizing and drying machines have been 
placed on the market, and even now comparatively 
few milk dealers are using them to the extent to 
which their merit entitles them. It is usually found 
that in milk-handling plants, both in those where 

171 



THE PASTEURIZATION OF MILK 

the milk is pasteurized and in those from which the 
milk is shipped in the raw state^ the sterilizing is 
very inadequately done. Usually the cans are 
washed by hand with a brush, and are then placed 
over a single jet of rinsing water and then over a 
single jet of live steam. The time occupied in 
both rinsing and steaming is usually but a few 
seconds. It often happens that the can covers are 
not steamed at all_, but are simply rinsed in water 
which is not over clean. When the cans which 
are to be returned to the patrons are washed, the 
steaming which the cans receive is so brief that it 
is almost negligible. This is not altogether the 
fault of the man who is washing the cans, for 
when milk is being delivered rapidly to the plant 
there is little time for long steaming. As a matter 
of fact, the cans require a more careful cleansing 
and sterilizing than do the bottles, since they are 
more likely to contain crevices and uneven sur- 
faces than are the bottles. If for any reason it is 
not feasible for a dealer to install an automatic 
can washer, it is still possible to obtain satisfac- 
tory results. An apparatus which is comparatively 
inexpensive may be constructed by providing a long 
table or runway of iron plate on which there are 

172 



FROM THE PRACTICAL VIEWPOINT 

installed two or three jets of water for rinsing cans, 
and also three or more jets of steam. Each jet 
should be provided with an automatic valve which 
will be opened by the weight or pressure of the 
can as it is placed over the jet. If flanges of iron 
or sections of gas pipe are so attached to the table 
that they will engage the flare of the can mouth 
as it is inverted over the table, it will be impos- 
sible to remove the can until it has travelled entire 
length of the table and has thus received the 
influx of water and steam from each of the jets. 
It is possible to so arrange the table that both 
cans and covers will be treated at the same time on 
the same table. This is accomplished by install- 
ing two sets of gas-pipe guides, one of them to 
hold the cans in place and the other of them to be 
just above the covers as they are pushed along the 
table, with the open end down. The cans referred 
to in this connection are the standard forty-quart 
cans used most largely in the East. 

Various machines are on the market which are 
so arranged that the cans, after having been well 
steamed, are also dried by means of a blast of 
heated air. This drying is important for two 
reasons. First, because the moisture which may 

173 



THE PASTEURIZATION OF MILK 

be left in the can renders the condition favorable 
for the growth of bacteria which have escaped de- 
struction, and second, because cans which are not 
dry are much more likely to become rusty. Rusty 
cans are hard to clean, and frequently become a 
loss to the owner because they soon wear out and 
are discarded. One form of can rinser, steamer 
and dryer is rather ingeniously arranged. The ex- 
haust steam, after having been used to operate a 
turbine-driven fan, is employed to sterilize the 
cans. The steam pipe which supplies the fan tur- 
bine passes in coils through an air chamber, and 
thus is used to heat the air which is forced by the 
fan into the cans after they have been sterilized. 
There is thus a very economical use of the steam, 
and the apparatus is also very compact. 

Cans, after they have been treated, should be 
stored in an inverted position until they are used 
for containing milk. If, however, they are thor- 
oughly dry, there seems to be no objection if the 
covers are tightly placed upon them and they are 
then stored without inverting. 

In determining what test to apply in order to 
ascertain whether or not milk containers are ster- 
ile, or sufficiently so for practical purposes, it 

174 



FROM THE PRACTICAL VIEWPOINT 

should be remembered that we are not dealing 
with laboratory conditions, and that therefore ab- 
solute sterility is not necessary, however desirable 
it may be from a theoretical standpoint. Our milk 
itself is not sterile, and if we can be assured that 
the containers are sufficiently clean so that they 
will not add any appreciable amount of bacteria to 
the milk, and that those which may be added are 
not of a pathogenic character, then health authori- 
ties should be satisfied. Remembering that a quart 
of milk contains about one liter of fluid, or 1,000 
cubic centimeters, it seems reasonable to allow the 
washed bottles to contain 1,000 bacteria. This 
would add but one bacterium to each c.c. of milk 
contained in the filled bottle. In like manner, 
40,000 bacteria in a washed can might add the 
same amount of bacterial contamination to the 
forty quarts of milk contained in the filled can. 
If none of these were of the coli group, it is proba- 
ble that no danger would result. As a matter of 
fact, with methods of cleansing which may be easily 
secured, the bacterial content of the containers will 
be much less than the allowable amount above re- 
ferred to. 



175 



THE PASTEURIZATION OF MILK 

Bottle-Filling 

The filling of the bottles is more an economic 
problem than a sanitary one. Of course, the care- 
ful cleaning and sterilization of the apparatus is 
necessary, no matter what kind of filler is used. 
Any failure in this respect may cause the milk to 
gather up bacteria while it passes through the 
bottling machine. This may cause annoyance, at 
least, when tests are made which indicate a high 
bacterial content. If, however, the cleaning is 
carefully done, the items which most interest the 
milk men are the questions of expense and of effi- 
ciency in operation. 

If a machine is operated by hand power, there 
is the question whether human power is cheaper 
than machine power. If automatically operated 
by outside power, either electric, steam or hydrau- 
lic, then the matter of bottle breakage, case dam- 
age, and loss of milk from broken bottles is an 
important consideration. A power-driven machine 
may or may not be slower in operation than hand 
power. The conditions surrounding each plant 
must be considered and decisions made in accord- 
ance with them. 

176 



FROM THE PRACTICAL VIEWPOINT 

The rotary filler and capper is coming into quite 
extensive use, with many features about it which 
appeal strongly to the milkman. 



Bottle-Capping 

It is important that milk, after having been 
pasteurized, shall not be recontaminated in any 
way. If containers are properly cleaned, the great- 
est danger of such reinfection lies in the practice 
of capping bottles by hand. When this method of 
capping is employed, the caps are frequently kept 
in open boxes beside the bottling machine, and they 
are sometimes kept in the pockets of the workmen 
who are capping the bottles. There is thus con- 
stant danger that the caps will become infected by 
dust in the air, by milk which is spattered upon 
them or by means of the hands of the persons who 
handle them. Men who handle bottle cases and at 
the same time work about machinery cannot easily 
keep the hands clean. The milk caps then suffer. 
If any germs of disease are about these employees 
then the danger becomes apparent. 

Some form of capping machine is desirable. Sev- 
eral such are on the market, and many of them 

177 



THE PASTEURIZATION OF MILK 

are doing satisfactory work. It is not necessary to 
describe the characteristics of each. Those are 
most desirable which fulfil the following conditions : 

First: The caps used should be stored in sterile 
containers or tubes before they are inserted in the 
machine. 

Second: A very small percentage of the bottles 
should be missed in capping. 

Third: They should be so constructed that they 
can be readily taken apart for cleaning, and they 
should have no concealed pockets or spaces where 
milk is likely to collect and become sour or decom- 
posed. 

Fourth : They should be strongly constructed in 
order that they may stand without breakage or dis- 
arrangement, the rather rough usage to which they 
are subjected. 

It is very desirable that milk bottles be sealed 
after they are filled. By sealing is meant that 
they be so protected that they cannot be opened 
without the fact being readily detected by the con- 
sumer. The desirability of this sealing process 
gets its force from two reasons: 

First: To prevent the drivers or others from 
opening the bottles and adulterating the milk. 

178 



FROM THE PRACTICAL VIEWPOINT 

Instances have been known where the drivers of 
rival companies have opened the bottles belonging 
to their competitors, and have fouled the milk in 
order to cast discredit upon the milk delivered by 
the rival concern. Other drivers have taken cream 
from the tops of bottles, and have filled the bot- 
tles with water. The cream they have sold for 
their own profit. Bottles which were effectively 
sealed could not be treated in this way. 

Second : To prevent possible contamination of the 
milk by means which are unintentional. The use of 
the usual paper plug cap leaves a space above the 
cap where dust and dirt and ice water from melt- 
ing ice, etc., can collect. Unless this is carefully 
washed off before the bottle is opened, it is likely 
to fall into the milk. If a bottle of milk which 
when filled has a temperature of say 50° to 55° 
is then placed in a case and covered with ice, the 
milk is cooled to perhaps S5° to 40°. This causes 
the milk to contract. The air in the space above 
the milk also contracts, and a suction is thus cre- 
ated. The water which collects on the top of the 
cap is then drawn into the bottle around the edge 
of the cap, taking with it some of the dirt which 
may have collected there. 

179 



THE PASTEURIZATION OF MILK 

The drivers of retail delivery wagons who han- 
dle the reins, care for the horses and then in de- 
livering milk grasp the bottles by the neck, are 
particularly likely to leave some dirt or contami- 
nating material upon the lips of the bottles over 
which the milk will be poured. Serious infection 
may result. Caps which are real seals and which 
at the same time protect the neck and lips are on 
the market, but are rather expensive. They are 
used by dealers upon special grades of milk, such 
as Certified, Grade A, etc., but are as yet too costly 
to be used upon the lower or common grade of 
market milk. A great many attempts have been 
made to devise a safe seal which shall be protec- 
tive and shall be inexpensive, but none have been 
very successful. A fortune awaits the man who 
can produce a satisfactory seal of this character. 

Paper Bottles 

For fifteen years or more various sorts of paper 
milk bottles have been upon the market. They 
have been made in various forms. Some were 
made of pulp which was formed into the shape of 
an ordinary bottle. Some have been crimped into 

180 



FROM THE PRACTICAL VIEWPOINT 

a bottle form from a single sheet of heavy paper. 
Others have been made of heavy waxed paper, 
through which the cream was visible. Some have 
had straight parallel sides. They have been made 
round and square; have been filled from the top, 
and have been filled from the bottom, but the suc- 
cess which has attended them has not been very 
marked, especially in the East. There are some 
firms in the western part of the country where 
their use has been rather extensive and where they 
are said to be satisfactory. 

The objections to their use has been — 1st, the 
expense. They are more costly than are glass 
bottles, when it is considered that the glass bottle 
is used repeatedly, while the paper one is used 
but once. 

2nd. Many of them are not strong enough to 
endure the heavy icing and rough handling to 
which they are subjected. 

3rd. Customers have been accustomed to seeing 
the cream in the bottle, and object to bottles where 
the cream is out of sight. 

4th. The constantly increasing cost of paper 
renders it questionable whether the equipment for 
using paper bottles may not prove to be available 

181 



THE PASTEURIZATION OF MILK 

for a short time only, and its expense thus 
wasted. 

5th. There is always uncertainty concerning the 
cleanliness of the bottles as delivered by the manu- 
facturers for use, and also as to whether or not 
the material used in the paper may affect the milk. 

There are undoubted advantages in the use of 
the paper container, among which are: 

1st. That the expense of handling and trans- 
portation will be lessened, on account of the lesser 
weight of the paper. 

2nd. The expense of washing returned bottles 
will be saved, since the paper container will be 
used but once. 

3rd. The possible danger which exists through 
the return of bottles from the public dumps, and 
from houses in which there are communicable dis- 
eases will be lessened if the single service container 
is used. 

4th. The danger from broken glass, which occa- 
sionally finds its way into the milk, will be ob- 
viated, and the wounds which are inflicted by 
broken bottles upon workmen who handle and wash 
them will be prevented. 



182 



FROM THE PRACTICAL VIEWPOINT 

Home Pasteurization 

Many physicians who thoroughly believe that 
milk should be pasteurized for infant feedings also 
recommend that this pasteurization be performed 
in the home, and that the pasteurized milk be 
fed as quickly as possible after the heating is 
completed. This method eliminates the possibil- 
ity of recontamination which may occur when milk 
is handled under commercial conditions, and it also 
insures that those bacteria which are not destroyed 
during the pasteurization process will have little 
opportunity for growth and increase between the 
pasteurization of the milk and its consumption. 

It is not the purpose of the writer to here de- 
scribe the various methods employed for home pas- 
teurization. Such information may be obtained 
from the pamphlets which are distributed by those 
responsible for maintaining the various infant-feed- 
ing stations located in our cities. Some of these 
stations are maintained by the municipalities and 
some by private individuals. Dr. Rosenau, in his 
book on "The Milk Question/' discusses this phase 
of pasteurization quite fully. 

Whatever method of home treatment is employed, 

183 



THE PASTEURIZATION OF MILK 



care should be taken that the heat is high enough 
and is maintained for a sufficient time to reach all 
parts of the milk, and so kill the pathogenic bac- 
teria. The heating medium should not be hot 
enough to cook or change the chemical characteris- 
tics of the milk or to impart to it a disagreeable 
odor or taste. 



184 



CHAPTER VI 

EFFICIENCY OF VARIOUS APPARATUS 

During the writer's experience in the actual 
operation of pasteurizing plants, a great many sam- 
ples of milk have been taken which have been ex- 
amined for their bacterial content in order to de- 
termine the efficiency of the various pasteurizing 
plants in the destruction of bacteria. These results 
have been tabulated, showing the bacterial content 
before, during and after pasteurization. In these 
tables the kind of apparatus are indicated by fig- 
ures only, no name of apparatus or of the manu- 
facturers being given. The dealers at whose plants 
the tests were made are indicated as "A," "B," 
"C," etc. Thus at a plant operated by dealer 
"A," for instance, a heater illustrated by Fig. 00, 
a holder like Fig. 00, and a cooler like Fig. 00 may 
have been employed. 

Lest the reader be misled as to the efficiency 
of certain definite forms of apparatus, and lest cer- 
tain manufacturers be led to feel that results ob- 
tained have failed to give justice to the apparatus 

185 



THE PASTEURIZATION OF MILK 

handled by them, the reader is warned that effi- 
ciency tests are sometimes misleading. It should 
be remembered that at least four factors enter into 
the causes which produce the effects indicated. 

1st. The character of the apparatus itself. 

2nd. The carefulness with which the plant is 
operated by those responsible for it. 

3rd. Whether the apparatus is thoroughly 
cleaned and sterilized. 

4th. The character of the milk treated. 

It is, of course, understood by all those familiar 
with bacteriological work that these are factors of 
error in the results which can never be entirely 
overcome. 

If apparatus is so constructed that the heating 
and holding and cooling are true to their indicated 
capabilities, then the results will be good — if the 
machine is properly operated and if it is clean. 
These factors being reliable, the results can be 
taken at their face value if the milk is of normal 
quality and does not contain, we will say, certain 
forms of bacterial life which are difficult to destroy. 

When results are good, it undoubtedly means 
that both the apparatus and its operation are sat- 
isfactory. If the results are bad, it is not always 

186 



FROM THE PRACTICAL VIEWPOINT 

easy to say whether the machine, its operation, or 
the milk is at fault. 

In regard to the milk itself, there are many fac- 
tors which must be taken into account when de- 
termining the efficiency of any apparatus. Esti- 
mates of machine efficiency based upon the 
percentage of bacteria destroyed are frequently 
misleading. It can be readily seen that if the bac- 
terial content of the raw milk is high, any good 
pasteurizer will kill a large percentage of the 
germs in the milk. For instance, if the original 
milk contained 5,000,000 bacteria per c.c, and 
after being pasteurized contains 100,000 bacteria, 
there would have been a reduction of 98 per cent, 
of the bacteria in the original milk. Milk contain- 
ing 100,000 bacteria per c.c. would not, however, 
be considered to be an entirely satisfactory prod- 
uct to place upon the market, especially if it con- 
tained organisms of the coli type. 

Again, let us suppose that the original milk con- 
tained 10,000 per c.c, and that by means of the 
pasteurizing process this number was reduced to 
1,000; such a milk would undoubtedly be a proper 
milk for consumption, although the percentage of 
reduction had been 90 per cent only. It is there- 

187 



THE PASTEURIZATION OF MILK 

fore plainly seen that the efficiency of pasteuriz- 
ing machinery, when expressed in percentage re- 
duction of bacteria only, must be taken with a 
great deal of reserve. It is necessary to know the 
character of the raw milk, and also to know if coli 
types are all destroyed. In speaking of the de- 
struction of coli, it should be remembered that 
germs of this group are not necessarily all danger- 
ous. In this connection they are used as indicators 
only. It is known that they are more difficult to de- 
stroy than are any of the pathogenic or disease-pro- 
ducing bacteria. If, therefore, the coli are all 
killed, it is safe to assume that no dangerous mi- 
crobes remain alive. While, if the coli are present 
in the finished product, there is a possibility that 
disease germs are also present. It is known pretty 
definitely that if milk is heated to 142-145° for 
thirty minutes, all coli will be destroyed. 

The following tables are compiled from very 
many tests made. When these tests were made 
there were three or four samples of milk taken at 
each point of examination; for instance, four sam- 
ples of raw milk were taken at the same time. 
When these were examined, the average of all the 
counts was determined. In the same way there 

188 



FROM THE PRACTICAL VIEWPOINT 

were four samples taken at the outlet of the heater, 
the holder, and so on. In the tables herewith com- 
piled, only the average counts are indicated, in or- 
der to avoid any bewildering mass of figures. It 
should be therefore borne in mind that bacteria 
counts here indicated are averages. 

In figuring out the percentage of reduction, 
the relation between the bacterial content of the 
raw milk and the milk as it leaves the holder is 
considered. It will frequently be found that the 
number of bacteria in the milk leaving the cooler 
is higher than when it leaves the holding appara- 
tus, and that this number is again increased when 
the milk enters the bottles and cans. Usually un- 
clean coolers, bottling machines and bottles are 
responsible for this increase. 

Not all of the types of apparatus which are 
illustrated and described in this book have been 
tested by the M^riter as to their efficiency in the de- 
struction of bacteria, and any omissions which may 
be observed in the tables are not due to any inten- 
tion on the part of the writer to slight any of them, 
or to any desire to call attention more forcibly 
to one kind of machine than to another. It simply 
means that the results of tests are not available. 

189 



THE PASTEURIZATION OF MILK 



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207 



CHAPTER VII 

CHANGES IN THE CREAM LINE DUE TO THE 
PASTEURIZATION OF MILK 

Dealers who have had experience in the pas- 
teurization of milk know that from time to time 
they have trouble with what is known in the trade 
as the "cream line" upon bottled milk. This may 
mean that the line of demarcation between the 
cream in the bottle and the skim milk just below it 
is indistinct and faint^ or it may mean that no 
cream at all is visible and the contents of the bot- 
tle has the same color all the way through. Again, 
it may mean that the apparent amount of cream 
upon the milk is lessened. Either one of these 
conditions is a reason for complaint on the part of 
the customers. Dealers are therefore anxious to 
obtain as great a volume of cream as possible upon 
the milk sold by them, and are also anxious to get 
the line of division as distinct as possible. Deal- 
ers are sometimes at a loss to know why milk will 
at one time show a good cream line, and at another 
time, when the conditions are apparently the same, 
the cream will be disturbed. 

208 



FROM THE PRACTICAL VIEWPOINT 

In I914<^ when the writer was connected with 
the New York City Department of Health, the 
Board of Health adopted certain modifications in 
the regulations which had been in force concerning 
the pasteurization of milk. Among these changes 
were different rules concerning the temperature to 
which milk must be heated and the length of time 
for which it must be held at this temperature if 
it was to be officially recognized as pasteurized 
milk. 

Prior to that time, the rules allowed a somewhat 
wide variation in the heating temperatures, and a 
corresponding variation in the length of time for 
which the milk should be held. Thus milk which 
was heated to 140° must be held at least twenty 
minutes, while milk heated to 158° need be held 
but three minutes. Between these extremes other 
temperatures and holding times were allowed. This 
sliding scale, as it might be called, allowed such a 
latitude that milkmen who sold milk in cans only, 
and were thus not much concerned with the cream 
line, could heat the milk to a high temperature and 
hold it for a short time. On the other hand, those 
dealers who sold bottled milk, and who were desir- 
ous to obtain as great a volume of cream as pos- 

209 



THE PASTEURIZATION OF MILK 

sible, could and usually did heat the milk to a low 
temperature and hold it for a comparatively long 
time. 

A desire for uniformity of methods in the treat- 
ment of milk led the authorities to adopt regula- 
tions, in accordance with which one standard for 
pasteurization only was applied, in all cases when 
milk was heated for market use. The rules thus 
adopted required all pasteurized milk to be heated 
to 145° for thirty minutes. 

Dealers who endeavored to comply with this rule 
complained that they found the cream line was 
affected, and that they could not comply with the 
public requirements without injury to their busi- 
ness. 

In an effort to ascertain to what extent the 
strict enforcement of the regulations would affect 
the commercial quality of the milk, the writer made 
an investigation. 

This investigation was not made with the inten- 
tion to determine what form of apparatus would 
do the best work, nor to make any extended or ex- 
haustive tests of any one form of apparatus un- 
der varying surroundings and conditions. The ob- 
ject was to see if it was possible and commercially 

210 



FROM THE PRACTICAL VIEWPOINT 

practicable to heat milk to 145° and hold it for 
thirty minutes with the machines in use in the city 
without seriously affecting the cream line. Any 
results and data secured do not warrant the con- 
clusions that the experiments indicate the essential 
superiority of any of the apparatus described. 

A little thought on the part of the reader will 
make it clear that so many factors enter into the 
problem that such conclusions would be unwar- 
ranted. 

In the same way that percentages of bacteria 
reduction mean little unless we possess all the 
data connected with the handling of the milk, 
so likewise percentages of cream upon pas- 
teurized milk are not alone of ultimate value as 
showing that one apparatus is more satisfactory 
than another. 

A series of tests was made at several of the 
pasteurizing plants in New York City at which 
different forms of apparatus were being used, the 
milk in these various plants being subjected to dif- 
ferent degrees of temperature for varying lengths 
of time. Samples of milk were taken to determine 
the amount of cream which appeared upon the 
bottled product. At the same time, the conditions 

211 



THE PASTEURIZATION OF MILK 

surrounding the handling of the milk were noted 
in order to determine if other factors aside from 
the temperature and holding time had any effect 
upon the cream line. 

In making the tests^ the samples of milk taken 
were set in standard cream gauge glasses and the 
actual percentage of cream showing upon the milk 
as indicated thereon was carefully noted. These 
tests were made during the early part of Decem- 
ber, 1914. 

First Test. — The first test was made at a plant 
in which the pasteurizing apparatus consisted of 
three tanks of the type shown in Fig. 13. Each 
tank had a capacity of about forty cans of milk, 
and after being filled the milk was heated by 
means of a revolving coil of pipe extending through 
the tank, through which coil hot water and steam 
were forced. After the milk reached the proper 
temperature, the steam was shut off in this coil 
and the milk was held at the same temperature 
for the desired length of time. It was then dis- 
charged into a cooler consisting of a tank in which 
were revolving disks, which is not here illustrated, 
and immediately cooled. Since it required con- 
siderable time for the tank to be fully emptied 

212 



FROM THE PRACTICAL VIEWPOINT 

after the discliarge was commenced, it is evident 
that a part of the milk was held in the tank for 
a considerably longer time than was that which 
was first discharged from the tank. In making the 
test, one tankfiil of milk was heated to a tempera- 
ture of 142° and was held thereat for about thirty 
minutes. The exact time of holding was not as- 
certained on account of the fact that the milk was 
being discharged from the tank at the time the 
inspection began. A sample was taken from this 
milk and placed in a cream gauge, which was then 
packed in ice and allowed to stand for four hours, 
at the end of which time 15 per cent, of cream ap- 
peared upon the cream gauge. 

A second sample was taken from one of the 
tanks in which the milk had been heated to a tem- 
perature of 116°, and held thereat for thirty-four 
and a half minutes. The sample here taken was 
allowed to stand packed in ice for four hours, at 
the end of which time 13 per cent, of cream ap- 
peared upon the gauge. A third sample was taken 
from the same tank, but it was taken from that 
milk which was last discharged from the tank. 
This milk, therefore, had been held in the tank for 
one hour and twenty-three minutes. This sample 

213 



THE PASTEURIZATION OF MILK 

was also set in ice for four hours and showed 8 per 
cent, of cream upon the gauge. 

A fourth sample was taken from a second tank 
in which the milk was heated to a temperature of 
146° and held thereat for exactly thirty minutes. 
This milk showed 15 per cent, of cream upon the 
gauge. 

The method of handling the milk at this plant 
should be noted. Milk was poured from the cans 
into a dumping tank on the ground floor. It was 
then pumped to a small tank upon the third floor 
of the building, thence flowed through a centrifugal 
clarifier, such as shown in Fig. 32, and then flowed 
directly into the pasteurizing tanks. 

Second Test. — A test was also made in another 
milk plant in which the same form of pasteurizing 
apparatus was installed. In this plant, the milk 
was pumped from the receiving vat on the gound 
floor into a tank upon the second floor, from which 
the milk flowed through a clarifier and was then 
discharged into a mixing vat, from which it flowed 
into the various pasteurizing tanks. The opera- 
tion of this plant was similar to that in the plant 
previously described, except that, in the first in- 
stance, the water which was forced through the 

214. 



FROM THE PRACTICAL VIEWPOINT 

heating coil of the tank was heated by means of a 
steam jet, injecting steam directly into the water 
pipe, wliereas, in the second instance, water was 
heated in a tank outside of the pasteurizing tank 
and was pumped, after the heating, directly into 
the heating coil, it being the belief that if the 
water was heated in this manner there was less 
danger of the milk becoming scorched on account 
of the water coil having been heated to a tempera- 
ture which was excessive 

At this second plant the first sample was taken 
from the raw milk before it had passed through 
the clarifier. This sample was allowed to stand 
in ice for eleven hours, at the end of which time 
19% per cent, of cream appeared upon the gauge. 
A Babcock test was made of this milk and it was 
found to contain 3.8 per cent, of butter fat. A 
second sample was taken, which was as nearly as 
possible from the same milk, after it had passed 
through the clarifier. This sample, after standing 
for eleven hours, showed 17 per cent, of cream on 
the gauge. This milk also contained 3.8 per cent, 
of butter fat. A third sample was taken from one 
of the pasteurizing tanks in which the milk was 
heated to 145° and was held in the tank for thirty- 

215 



THE PASTEURIZATION OF MILK 

three minutes, at which time the temperature was 
found to be 11214° F. This sample, upon being 
set, showed 12 per cent, of cream in the cream 
gauge and contained 3.8 per cent, of butter fat. 
The fourth sample was taken from the same tank 
of milk, but when the tank was nearly empty. 
The milk had been standing in this tank for one 
hour and twenty minutes. It had been, however, 
cooled to a temperature of 60° F. by means of 
cold water pumped through the revolving coil. 
A sample of this milk, upon setting, showed 15 
per cent, of cream in the cream gauge and con- 
tained 3.8 per cent, of butter fat. 

It was thought possible that the speed of cool- 
ing of milk might have an effect upon the cream 
line. Therefore two samples of milk were taken, 
one of which had a temperature of 135° F. This 
sample was allowed to stand un-iced until cooled 
by air contact to a temperature of about 40° F. 
The second sample of milk was taken from the 
same batch of heated milk, but this sample was 
taken after the milk had been quickly cooled in 
the cooling apparatus to a temperature of 32° F. 
After setting, these two samples showed no appre- 
ciable difference in the cream content. This indi- 

216 



FROM THE PRACTICAL VIEWPOINT 

cated that the speed of cooling had little or no 
effect upon the rising of the cream in the milk. 

The tests made at these two plants indicated 
that it was entirely possible to heat milk to 145° 
F. and hold it for thirty minutes without materially 
affecting the volume of the cream contained in the 
bottled milk, and that milk heated to 145° F. 
showed the same amount of cream as that which is 
heated to 142° F. 

Third Test. — A test was made at another plant 
where the same form of apparatus for pasteuriz- 
ing was in use. During this test a sample was 
taken from a tank in which the milk was heated 
to a temperature of 141° and held there for sixty 
minutes. This sample, after standing a sufficient 
length of time, showed a cream content of 15 per 
cent. A second sample was taken of raw milk 
which had already been passed through the clari- 
fier, and this milk was found to contain 1 5 per cent, 
of cream. A third sample was taken from a tank in 
which the milk had been heated to 145° and held 
thereat for sixty minutes. This milk, after stand- 
ing, showed no cream at all upon the cream gauge. 

The results here obtained did not correspond 
with those obtained at the two other plants where 

217 



THE PASTEURIZATION OF MILK 

the same apparatus was in use. No apparent rea- 
son could be seen for the variation. Milk at this 
plant, as received from the patrons, was allowed 
to flow from the weigh vat into the mixing vat, 
from which it was pumped to a vat upon the sec- 
ond floor, thence it flowed into a clarifier, from 
which it was discharged into a large mixing vat on 
the same floor. It then flowed by gravity to the 
pasteurizing vats on the first floor. 

Fourth Test. — A further test was made at an- 
other pasteurizing plant, in which the milk was pas- 
teurized by means of a heater and holder, shown 
in Figs. 5 and 22. In this heater the milk was 
forced between two concentric cylinders, in each 
of which hot water was contained, having a tem- 
perature of 159°. The milk while being heated 
was kept in agitation by the rapid revolution of 
one of the cylinders above referred to. After 
heating, the milk flowed by gravity into a series of 
insulated tanks, in each of which it was held for 
twenty-four minutes. On account of the fact, how- 
ever, that milk as discharged from the heater 
flowed first into a tank from which the various 
holding tanks were filled, and on account of the 
added fact that when these tanks were discharging 

218 



FROM THE PRACTICAL VIEWPOINT 

the milk, it flowed into a second tank before being 
convej'^ed to the cooling apparatus, it is probable 
that the milk was actually held at the highest tem- 
perature for a period of at least twenty-seven 
minutes. 

A sample was taken from the raw milk before 
being clarified. This milk, upon setting, was found 
to contain 15 per cent, of cream and to have a fat 
content of S.9 per cent. A second sample was 
taken from milk which had been heated to 145° 
F., and, after holding, was set and found to con- 
tain 10% per cent, cream and 3.9 per cent, butter 
fat. A third sample was taken from milk which 
was heated to 144°, and was found to contain 8 
per cent, of cream and 3.9 per cent, butter fat. A 
fourth sample was taken from milk which was 
heated to 142°, and was found to have a cream 
content of 8 per cent, and 3.9 per cent, butter fat. 

These results indicated that the milk which was 
heated to 145° contained a greater percentage of 
cream, by volume, than that which was heated to 
142°. The reason for this was not apparent. The 
milk pasteurized at this plant was received from 
the railroad in cans which had been shipped from 
the country. The milk was dumped from these 

219 



THE PASTEURIZATION OF MILK 

cans into a large dump vat, from which it was 
pumped to a receiving vat upon the second floor 
and was thence allowed to flow through a clarifier, 
from which it was discharged into a large mixing 
vat and thence flowed directly to the milk heater. 

Fifth Test. — This test was made at a plant at 
which the milk was pasteurized by means of a 
heater somewhat similar to that shown in Fig. 3. 
The holder was like Fig. 21. In this heater the 
milk is forced between two water-heated cylin- 
ders, in one of which the water was at a tempera- 
ture of l65°, and in the other of which the tem- 
perature of the water was nearly at the boiling 
point. The milk, while being heated, was kept in 
agitation by means of a revolving arm, which was 
so arranged that it moved between the two heat- 
ing surfaces. The milk, after heating, was held 
in a series of eight water-jacketed tanks, the water 
surrounding the tanks being kept at a temperature 
of from 145° to 150° F. The milk, while in this 
holding tank, was kept in agitation by means of re- 
volving metal stirrers. 

A sample was first taken from one of the hold- 
ing tanks in which the milk was heated to a tem- 
perature of 143° F. and held there for thirty 

220 



FROM THE PRACTICAL VIEWPOINT 

minutes. This sample, when set, was fomid to 
have 11 per cent, of cream in volume, and the but- 
ter fat content was 3.7 per cent. A second sample 
was taken from a holding tank in which milk had 
been heated to a temperature of 147° and held 
for thirty minutes, the temperature of the milk at 
its discharge being 146°. This milk showed 4 per 
cent, of cream and a fat content of 3.8 per cent. 
A third sample was taken from a tank in which 
milk was heated to 145° and held for thirty 
minutes. This milk, when set, showed 7 per cent, 
of cream and 3.7 per cent, butter fat. A fourth 
sample was taken from milk which had been heated 
to 146° and held for thirty minutes. This milk 
showed 3 per cent, of cream and 3.9 per cent, but- 
ter fat. 

These results indicate that with this form of ap- 
paratus the cream line was seriously interfered 
with, even at a temperature as low as 143°. The 
milk, as received in this plant, was poured from 
cans into a receiving tank upon the upper floor 
of the building from which it flowed to an appa- 
ratus on the floor below in which it was preheated 
to 60° F. It then passed through centrifugal 
clarifiers from which it was discharged into a large 

221 



THE PASTEURIZATION OF MILK 

tank upon the receiving floor. From this tank it 
flowed by gravity to the pasteurizers on the floor 
below. 

Sixth Test. — This test was made at a plant in 
which the milk was heated by means of an appa- 
ratus shown in Fig. 11, where the milk is heated 
by means of what is known as a Multitube Heater. 
In this form of heater a series of large tubes are 
so arranged that several smaller tubes extend 
through them. The milk is forced through the 
inner tubes, while hot water is forced through the 
large surrounding tubes. After heating, the milk 
is discharged into a series of eight holding tanks 
similar to those described in test No. 5. The water 
which is used to heat the milk in this apparatus is 
itself heated in a tank outside of the milk heater 
and is kept at a temperature varying between 144° 
and 163°, the temperature rarely exceeding 154°. 
From this tank the water is pumped to the milk- 
heating apparatus. 

The conditions at this plant were apparently fa- 
vorable for securing good results. The fact that 
the temjjerature of the heating water was carefully 
controlled, made it impossible to superheat or 
scorch any of the milk. The first sample of milk 

222 



FROM THE PRACTICAL VIEWPOINT 

was taken from raw milk before it was clarified. 
This sample, when set, showed 131/2 per cent, of 
cream and 3.4 per cent, butter fat. The second 
sample was taken from one of the holding tanks 
in which the milk was heated to a temperature of 
146° and held thereafter for tliirty minutes. This 
sample, when set, showed no cream whatever on 
the cream gauge, the fat being evidently evenly 
distributed throughout the entire body of the milk. 
This milk contained 3.5 per cent, of butter fat. 
A third sample was taken from one of the holding 
tanks in which the milk was heated to 143° F. 
and held for thirty minutes. This milk showed, 
upon standing, 10 per cent, of cream and 3.7 per 
cent, butter fat. Sample No. 4 was take^ from a 
tank in which the milk was heated to 146° F. and 
held for thirty minutes. This sample showed 5 
per cent, of cream and 3.35 per cent, butter fat. 

The results here obtained indicate that with this 
apparatus if the milk was heated above 143° the 
cream would be seriously affected. 

Seventh Test. — A test was made at still an- 
other plant in which the milk was heated by means 
of the pasteurizer shown in Fig. 9- In this appa- 
ratus the milk is forced through a series of pipes 

223 



THE PASTEURIZATION OF MILK 

which are enclosed in a large chamber which is 
filled with hot water. The apparatus somewhat 
resembles the tubular boiler. After heating, the 
milk is held in three upright cylindrical Park hold- 
ing tanks, the milk passing through the entire se- 
ries. In this holding apparatus tests previously 
made indicated that milk is held for from thirty- 
live to forty minutes. 

In making this test, the first sample was taken 
from the raw milk. This sample, when set, showed 
14 per cent, of cream and 3.8 per cent, butter fat. 
A second sample was taken from milk which was 
heated to a temperature of 143° and held for from 
thirty-five to forty minutes. This sample, when 
set, showed 14 per cent, of cream and 3.8 per cent, 
butter fat. In order to vary the experiment the 
temperature of the milk entering the holder was 
then raised to 145°, at which temperature the milk 
was maintained until the process of pasteurizing 
was completed for the day. The milk in the filled 
holding tanks was allowed to stand for thirty 
minutes and a sample was taken from that which 
was being discharged from the holding tank, which 
showed, on standing, 14 per cent, of cream and 
3.85 per cent, butter fat. A fourth sample was 

224 



FROM THE PRACTICAL VIEWPOINT 

taken from the milk which was last discharged 
from the holder. This milk had been in the holder 
for exactly sixty minutes. Upon standing, this 
milk showed 9 per cent, of cream and S.7 per cent, 
butter fat. 

These results indicated that milk could be heated 
to 145° and held for thirty minutes without any 
injurious effect upon the cream line being pro- 
duced, but that if the milk was held for an hour, 
the cream line was considerably affected. 

Eighth Test. — A further test was made at a 
pasteurizing plant in which the milk was heated 
by means of the heater shown in Fig. 7, and held 
in the holder illustrated in Fig. 27. In this appa- 
ratus the milk is forced through a series of pipes 
which are themselves enclosed in a larger pipe 
through which hot water is forced. The holding 
apparatus consists of a series of large tubes 
through which the milk is allowed to flow. It re- 
quires about thirty-five minutes for the milk to be 
discharged through the holding tubes. 

A sample was taken from the raw milk, before 
clarifying. This was found to contain 15^2 per 
cent, of cream and 3.5 per cent, butter fat. A sec- 
ond sample was taken from milk which had been 

225 



THE PASTEURIZATION OF MILK 

clarified, and this was found to contain 12 per cent, 
cream and 3.6 per cent, butter fat, there being an 
apparent reduction of 3% per cent, of cream vol- 
ume due to the clarifying process. A third sam- 
ple was taken from milk leaving the holder at a 
temperature of 142°. This was found to contain 
8 per cent, cream and 3.7 per cent, butter fat. A 
fourth sample was taken from milk leaving the 
holder at a temperature of 145°. This showed 7 
per cent, of cream and 3.6 per cent, butter fat. 

The results here obtained indicated that milk 
which is heated to 145° shows about the same 
amount of cream, by volume, as that which is 
heated to 142°, but the milk heated to either tem- 
perature showed but little more than half the 
amount of cream which was found in the raw 
milk. 

The milk at this plant was received in the 
dumping tank on the first floor, from which it was 
pumped to a tank upon the pasteurizing floor, and 
thence flowed through a centrifugal clarifier into 
the mixing tank. From this tank it was pumped 
through the heater and holder, and after being 
discharged from the holder was again pumped 
through the cooler. 

226 



FROM THE PRACTICAL VIEWPOINT 

Summary of Results 

All the tests made indicate that when milk is 
cleaned by a centrifugal clarifier, the volume of 
cream in the milk suffers a reduction of 2 per cent, 
to 3 per cent. 

The number of tests made was probably not 
sufficient to warrant the drawing of absolutely 
definite conclusions. It was evident, however, that 
the volume of cream in bottled milk was influenced 
by various factors, some of which are apparently 
little understood. These factors include: 

(1) The temjDerature to which the milk is 
heated. 

(2) The length of time for which milk is held 
at the high temperature. 

(3) The temperature of the heating medium 
with which the milk comes in contact during the 
heating process. 

(4) The clarification of the milk. 

(5) The type of apparatus used in treating the 
milk. 

(6) The amount of agitation to which the milk 
is subjected, especially while hot. 

This last factor has a greater influence upon 

227 



THE PASTEURIZATION OF MILK 

the cream line than is ordinarily appreciated. It 
has been stated to the writer, that in one instance 
where the cream line was materially reduced dur- 
ing the pasteurization process, the experiment was 
made of reducing the speed of the agitator which 
kept the hot milk in motion. After the speed had 
been so reduced it was found that the cream line 
upon the milk resumed its normal character. 

It will also be noted from the foregoing descrip- 
tion of the various methods of handling milk that 
in those plants where there was most agitation of 
the milk, and especially where the pumping of 
hot milk was practiced, the most difficulty with the 
cream line was experienced. There are possibly 
other factors which affect the cream line, among 
which may be: 

1st, the age of the milk before pasteurization. 

2nd, the grade of cows from which the milk was 
produced. 

3rd, the fact that milk has or has not been frozen 
before being treated. 

The tests made proved that it is entirely pos- 
sible, under the most favorable conditions, to heat 
milk to 145° and hold it for thirty minutes without 
producing any injurious effect upon the cream line. 

228 



FROM THE PRACTICAL VIEWPOINT 

It is also doubtless true, however, that with some 
types of apparatus in use by the milk dealers and 
with some conditions under which milk is handled, 
a real difficulty is experienced in obtaining satis- 
factory results. 

The chart shown in Fig. 34, drawn by Dr. North, 
indicates graphically the temperatures and holding 
times within which it is safe to heat milk without 
affecting the cream line. Such a chart cannot show 
the other factors which also affect the results, such 
as the amount of agitation, etc. 

If the milk is being heated and an attempt is 
made to keep the milk at a temperature no lower 
than 145° F., it is almost certain that the tempera- 
ture will at times reach from 146 to 148° or higher, 
and that it will at times be held longer than thirty 
minutes. It is almost mechanically impossible to 
so control the temperature of milk while heating 
that there will not be considerable variation. 

The agitation probably has the effect of break- 
ing up the fat globules into smaller masses. Since 
each globule of fat is surrounded with a film of 
casein or skim milk, which is heavier than the fat, it 
is evident that as the mass of fat becomes smaller, 
the proportional amount of the surrounding skim 

229 



THE PASTEURIZATION OF MILK 



TIME. AMD TLMPLRATURE. FOR 
ntf MILK PASTEURIZATION. 




/O' 10' 30' 40' 

Tl ME. IN MINL/TE-d 

Fig. 34 
230 



FROM THE PRACTICAL VIEWPOINT 

milk becomes greater, till we reach a point when 
the buoyant fat cannot lift the heavier envelope, 
and our balloon of fat stays down. 

Just why the high heat and the long holding 
scatters the fat permanently through the body of 
the milk is not so clear. It may be due to chemical 
changes which occur. 

In the pasteurizing equipment described on 
pages 124 and 131 it is claimed that the superheat- 
ing of the held milk has a beneficial effect upon 
the cream lines. 

The tables following show graphically the re- 
sults of the tests made. They indicate the varied 
conditions under which milk was handled in the 
various tests and the percentage of the cream upon 
each sample as well as the percentage of butter fat 
which was determined by the Babcock test. 



231 





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239 



CONCLUSION 

In conclusion, it may not be amiss to say that all 
the indications lead to the conviction that the pas- 
teurization of milk is not, as some have claimed, a 
fad. It is coming more and more into use, as a 
recognized sanitary measure, which is at present 
necessary. Whether a time may come when it will 
be safe for large commimities to consume their 
milk unheated is a question which at present is not 
a subject for practical consideration. The South 
and West, which have been slow to recognize the 
value of pasteurization, are coming into line, and 
the teaching of practical methods of handling ap- 
paratus used in pasteurizing milk is a wise thing 
for the dairy schools to take up. Practical meth- 
ods of controlling the actual operation of pasteuriz- 
ing plants should be taught, and instruction should 
be available for inspectors employed by munici- 
palities, as well as for those who are to become 
such inspectors, in order that they may be equipped 
to render the most useful service to the com- 
munities when they assume their duties. 

240 



THE PASTEURIZATION OF MILK 



Other methods may be discovered by which milk 
may be rendered safe with less trouble and ex- 
pense, but none such are now in sight, and until 
they appear our towns and cities must depend upon 
the proper application of heat to render milk safe 
as food. 

It is due to the citizens that the actual treatment 
of the milk be so intelligently supervised and con- 
trolled that it will in reality be as safe as the 
people have a right to expect. 



241 



INDEX 
A 

PAGE 

Adulteration of Milk 5,6 

Agricultural Department 2 

Ahlborn 11 

Air-compressors 135 

Avers (and Johnson) 9? 86, 155 

B 

Boards of Food Control 2 

Bottle-capping 177-180 

Bottle-cleaning 163-175 

Bottle-filling 176 

Bottles, Paper 180-182 

Bovine Tuberculosis 18-22 

C 

Capping Bottles 177-180 

Chemical Changes 27 

Cleaning and Clarifying 150-155 

Color Test 115,116 

Compressed Air 135 

Conclusion 210 

243 



INDEX 

PAGE 

Containers, Washing of 163-175 

Control (Official) of Pasteurization 32-34 

Controllers, Temperature 27, 133-140 

Cooling 155 

Coolers, Open 155-160 

Tank 160-161 

Tubular 162 

Cream Line 21, 29, 208-239 

D 

Department of Health, Reprints 9 

New York City 27, 43, 94, 209 

Denmark 11, 12 

E 

Efficiency of Apparatus 185-207 

Electric Process 90, 91 

Enzymes 30 

F 

Filling Bottles 176 

Fresca 11 

G 

Geneva Experiment Station 19, 158 

244 



INDEX 
H 

PAGE 

Health Department 2 

New York City 9, 27, 43, 94, 209 

Heaters 43 

First Type , 44-47 

Second Type 47-56 

Third Type 56-65 

Fourth Type 65-77 

Fifth Type 77-89 

Holding Time, Method of Calculation... 96,103 

Holders 94-107 

Absolute Type 94-1 1 1 

Points to be Observed in 108, 109 

Continuous or Flow Type 111-132 

Disturbances of Holding Time. .113, 114 

Horizontal Tank 124-126 

Park Tank 1 1 1-123 

Testing of Holding Time 115, II6 

Tubular 126-129 

Home Pasteurization 183, 184 

I 

Infection of Milk 4, 5, 18-22 

245 



INDEX 

J PAGE 

Jacob! 13 

Johnson 9^ 86, 155 

K 

Kiilp 158 

M 

Milk Dealers' Organizations 6, 7 

Milk, Changes Due to Pasteurization. ... 27 

Methods of Official Control 32-34 

N 
New York City 9, 15, 27, 43, 94, 209, 212 

O 

Ozone Treatment 92 

P 

Park 20, 23, 111 

Pasteur 10 

Paper Bottles 180-182 

246 



INDEX 

PAGE 

Pasteurization in General 1-42 

Pasteurization Literature 7—9 

Pasteurization, Home 183, 184 

Regulations 27 

Pasteurized Milk, Requirements for Secur- 
ing Good Results 31, 32 

Pasteurizer, Danish 11, 12 

Pasteurizing Plant, Requirements for Sat- 
isfactory Equipment 36-42 

Pasteurizing in Vacuum Pans 89, 90 

Percentage of Bacterial Reduction 185-207 

Public Health Reports 18 

Pumjos 39 

R 

Recorders — Temperature 140-149 

Reid 11 

Rosenau, M. J 9, 22, 23, 25, 183 

Ruehl (and Kulp) 158 

S 

Schores 25, 27 

Septic Sore Throat 17, 18 

Sheele 10 

247 



INDEX 



PAGE 

Sohxlet 13 

Storch Test 32 

Superheating of Milk 131 

T 

Temperature Controller 27, 133-140 

Temperature Test, Holding Tanks 115,116 

Temperature Recorders 140-149 

Testing Cleaned Containers 174, 175 

Testing of Holding Time 115, ll6 

Thermal Death Point 27 

Tuberculosis 12, 18-21 

Typhoid Fever 17 

U 

Ultra Violet Rays 92 

V 

Vacuum Pans 89, 90 

W 

Washing of Containers 163-175 

Winslow 18 

248 




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